404 Error Page:
Also called: 404 Error: File Not Found. A three-digit code that appears when a client isn't able to connect with a server. The first "4" indicates a client error, such as a mistyped URL. The following two digits indicate the specific error encountered.

ActiveX:
A not-very-distinct set of technologies developed by Microsoft for sharing information among different applications. ActiveX is an outgrowth of two other Microsoft technologies called OLE (Object Linking and Embedding) and COM (Component Object Model).

Affiliate Program:
An automated marketing program where Web merchants recruit Webmasters to place the merchant's banner ads or buttons on their own Web site. Webmasters will receive a referral fee or commission from sales when the customer has clicked the affiliate link to get to the merchant's Web site to make the purchase.

ANSI:
American National Standards Institute. Founded in 1918, it's a voluntary organization composed of over 1,300 members (including all the large computer companies) that creates standards for the computer industry.

Apache
A public-domain, open source Web server. The first version of Apache was developed in 1995. The development of Apache is similar to development of the Linux Operating System.

ASCII:
American Standard Code for Information Interchange. Pronounced ask-ee, it's a code for representing English characters as numbers.

ASP:
Application Service Provider. A third-party entity that manages and distributes software-based services and solutions to customers across a wide area network from a central data center according to the application being used, such as high or low volume business, specific business, and a local or regional business.

Auto-Responder:
An Internet-based system that automatically stores and sends electronic information to subscribers. The information can be in the form of emails, sales letters, or ebooks or any other electronic format.

BIT:
Binary Digit. The smallest unit of information on a machine. The term was first used in 1946 by John Tukey. A single bit can hold only one of two values: 0 or 1. (See BYTE).

BLOG:
Web Log. An online forum where authors enter their opinions about issues, and allows the readers to respond by entering their own opinions.

BROADBAND:
A type of data transmission in which a single medium (wire) can carry several channels at once. Cable TV, for example, uses broadband transmission. In contrast, baseband transmission allows only one signal at a time. Most communications between computers, including the majority of local-area networks (LAN), use baseband communications.

BYTE:
Binary Term. Composed of 8 bits. Can hold one character. Ex: The letter "a" is composed of 8 bits, ie. "a" = 1 byte = 8 bits of memory. (See BIT).

• Kilobytes - One thousand bytes.
• Megabytes - One million bytes.
• Gigabytes - One billion bytes.
• Nanobytes - Ten billion bytes.

CA:
Certificate Authority. A trusted third-party organization or company that issues digital certificates used to create digital signatures and public-private key pairs.

CABLE:
A broadband Internet connection that is designed to operate over cable TV lines. Cable modem download speeds are typically up to 2 times faster than 1.5Mbps DSL. (See DSL).

CD-ROM:
Compact Disc - Read Only Memory. Capable of storing large amounts of data -- up to 1GB, although the most common size is 650MB (megabytes). A single CD-ROM has the storage capacity of 700 floppy disks, enough memory to store about 300,000 text pages. (See DVD and Floppy Disk).

Certificate:
An attachment to an electronic message used for security purposes. The most common use of a digital certificate is to verify that a user sending a message is who he or she claims to be. A certificate is granted by the Certificate Authority (CA). The most widely used standard for digital certificates is X.509.

CGI:
Common Gateway Interface. A specification for transferring information between a World Wide Web server and a CGI program. A CGI program is any program designed to accept and return data that conforms to the CGI specification. The data in a form: name, address, age, birthday, etc. is an example of data that can conform to cgi specs. CGI allows the data to be transferred to a database where it is kept in an orderly fashion.

Chicklet:
A feed button that normally contains a feed reader logo and has a specific blog or feed information attached to it. It is coded to easily allow users to subscribe to a feed.

CHMOD:
Change Mode, or Change Modulator. A command, in either letters of numbers, that changes the usability of a file. There are three modes a file can have turned on or off: read ability, write ability, and execute ability. Each mode can be set for either the owner, the members of the owner's group, or all users. Usually performed in one's FTP program.

Cloaking:
Hiding something to either make it look like something else, or not allow it to be seen at all. Also called stealth. There are two reasons to cloak. It may be used by some Internet marketers to deceive the public or, cloaking can also be used to protect your code from the bad guys out on the net who think nothing of stealing your work and hard-earned income. While cloaking for deception is bad, cloaking for protection is not only necessary and good, it's just plain smart.
Caution: Parenthetically, there are some very influential people on the net who don't want you to cloak for any reason, and who will do anything they can to stop you. It's unknown why they act this way, though there is a suspicion that either they are intellectually myopic and can't ascertain the difference between the two methods, or they themselves use cloaking but don't want anyone else to have the advantage of doing so.

Clock Speed:
How fast a computer computes. Measured in megahertz. A megahertz is equal to one million cycles per second. A computer that has a clock speed of 200 Mhz can compute at 200 million cycles per second.

COM:
Component Object Model. Microsoft's Object-oriented programming model that defines how objects interact within a single application or between applications. An open standard that specifies how components are "glued" together and how they interoperate. An infrastructure that allows objects to communicate between processes and computers. Also known as ActiveX it's a Microsoft technology for software componentry. Implemented on several platforms, it is primarily used with Microsoft Windows. Used for creating and running interactive multimedia (text, graphics, video, and sound files) on websites. ActiveX technology allows users to view Word and Excel documents directly in a browser. Also used for drop down menus, radio buttons, scroll bars and more.

Density:
How tightly information is packed together on a storage medium (tape or disk).

• Single-Density: A low-density floppy disk (Now obsolete).
• Double-Density: A floppy disk that has twice the storage capacity of a single-density floppy. Single-density disks are now obsolete. Double-density 5¼-inch disks for PCs can hold 360K of data. Double-density 3½-inch disks can hold 720K.
• High-Density: A high-quality floppy disk capable of holding more data than a double-density disk. High-density 5¼-inch disks for PCs can hold 1.2MB (megabytes) of data. High-density 3½-inch disks can store 1.44MB.

DLL:
Dynamic Link Library. An executable code module for Microsoft Windows that can be loaded on demand and linked (dynamically) when needed, and then unloaded when the code is no longer needed. Several different programs reuse the same DLL instead of having that code in their own file, this dramatically reduces required storage space. Used to integrate multiple programs and provide the impression of a single product. Not a stand-alone software package, but intended to be run from other programs.

DOS:
Disk Operating System. The original operating system from Microsoft. It was comprised of just a big black screen with white type. It's where all the work on the computer was originally performed. It's considered inadequate for today's computer systems, but can still is of great benefit if learned and understood properly. The advice is - if you don't know how to use it, stay out of it (unless you want to really screw up your computer).

Drivers:
Basically a driver is a program that controls how other devices work. Every device, whether it be a printer, disk drive, or keyboard, must have a driver program. A driver acts like a translator between the device and programs that use the device.

DSL:
Digital Subscriber Lines. Used only for connections from a telephone switching station to a home or office. DSL offers users a choice of speeds ranging from 144 Kbps to 1.5Mbps. (See CABLE).

DTD:
Document Type Definition. A DTD states what tags and attributes are used to describe content in an SGML, XML or HTML

DVD:
Digital Versatile Disc or Digital Video Disc. A type of optical disk technology similar to the CD-ROM. A DVD holds a minimum of 4.7GB of data, enough for a full-length movie and equal to 4 to 6 CD-ROMs. (See CD-ROM and Floppy Disc).

Encryption:
The process of scrambling stored or transmitted information so that it is unintelligible until it is unscrambled by the intended recipient.

• AES:
  Advanced Encryption Standard, a symmetric 128-bit block data encryption technique. The U.S government adopted the algorithm as its encryption technique in October 2000, replacing the DES encryption it used. AES has a fixed block size of 128-bits and a key size of 128, 192, or 256-bits.
• DES:
  Data Encryption Standard, a popular symmetric-key encryption method developed in 1975 and standardized by ANSI in 1981 as ANSI X.3.92. DES uses a 56-bit key and uses the block cipher method, which breaks text into 64-bit blocks and then encrypts them.
• IDEA:
  International Data Encryption Algorithm. It and DES are the two most commonly used symmetric techniques for encryption.
  
• SSL:
  Secure Sockets Layer. A protocol developed by Netscape for transmitting private documents via the Internet. SSL uses a cryptographic system that uses two keys to encrypt data − a public key known to everyone and a private or secret key known only to the recipient of the message.
• TSL:
  Transport Layer Security. A protocol that ensures privacy between communicating applications and their users on the Internet. When a server and client communicate, TLS ensures that no third party may eavesdrop or tamper with any message. TLS allows the server and client to authenticate each other and to negotiate an encryption algorithm and cryptographic keys before data is exchanged. TLS is the successor to the Secure Sockets Layer (SSL).
• Public Key Encryption:
  A "key" is a password or a group of words. In public-key encryption, two different mathematically related keys (a key pair) are used to encrypt and decrypt data. Information encrypted with one key may only be decrypted by using the other half of the key pair. It was invented in 1976. It is called asymmetric encryption because it uses two keys (As opposed to one key in symmetric encryption).
• Private Key Encryption:
  In private-key encryption, the sender and receiver of information share a secret--a key that is used for both encryption and decryption.

• .com: A command file.
• .txt: A text file.
• .exe: An executable program.
• .zip: A compressed file.
• .dir: A directory file.

Favicon:
Favorite Icon. A customized icon designed specifically for a web site (see the left side of the address bar above for a great example of a favicon).

FAT:
File Allocation Table. A table that the operating system uses to locate files on a disk. Due to fragmentation, a file may be divided into many sections that are scattered around the disk. The FAT keeps track of all these pieces.

Floppy Disc:

• 5¼-inch: The disk size before 1987. This type of floppy was capable of storing between 100K and 1.2MB (megabytes) of data.
• 3½-inch: The present disk size (though fading fast - as of 2007). A storage capacity from 400K to 1.4MB of data. The most common sizes for PCs are 720K (double-density) and 1.44MB (high-density). (See CD-ROM and DVD).

Graphics:

• BMP:
  Bit-Mapped. A program that represents pictures as bit maps (ie. zeros and ones mapped in the shape of the graphic).
• GIF:
  Graphics Interchanged Format. A bit-mapped graphics file format. GIF supports color and various resolutions. It also includes data compression, but because it is limited to 256 colors, it is more effective for scanned images such as illustrations rather than color photos.
• JPEG:
  Joint Photographic Experts Group. JPG is a lossy (data) compression technique that is designed to compress color and grayscale continuous-tone images. The information that is discarded in the compression is information that the human eye cannot detect. JPG images support 16 million colors and are best suited for photographs and complex graphics. The user typically has to compromise on either the quality of the image or the size of the file. JPG does not work well on line drawings, lettering or simple graphics because there is not a lot of the image that can be thrown out in the lossy process, so the image loses clarity and sharpness.
• PNG:
  Portable Network Graphics. PNG was developed as a patent-free answer to the GIF format but is also an improvement on the GIF technique. An image in a lossless PNG file can be 5%-25% more compressed than a GIF file of the same image. PNG builds on the idea of transparency in GIF images and allows the control of the degree of transparency, known as opacity. Saving, restoring and re-saving a PNG image will not degrade its quality.
• TIFF:
  Tagged Image File Format. A file format for mainly storing images, including photographs and line art. TIFF is a popular format for high color depth images, along with JPEG and PNG. TIFF format is widely supported by image-manipulation applications. TIFF graphics can be any resolution.
• Raster Graphics:
  Represents graphical images through bit maps. A data file or structure representing pixels (dots). Raster graphics are distinguished from vector graphics (See) in that vector graphics represent an image through the use of geometric objects such as curves and polygons. Raster graphics cannot be scaled to a higher resolution without loss of apparent quality.
• Vector Graphics:
  Same as Object-Oriented Graphics. Software and hardware that use geometrical formulas to represent images. Programs that enable you to create and manipulate vector graphics are called draw programs, whereas programs that manipulated bit-mapped images are called paint programs. Vector-oriented images are more flexible than bit maps because they can be resized and stretched.

HTTP:
HyperText Transfer Protocol, the underlying protocol used by the World Wide Web. HTTP defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands.

IP:
Internet Protocol. IP specifies the format of packets, also called datagrams, and the addressing scheme. Most networks combine IP with a higher-level protocol called Transmission Control Protocol (TCP), which establishes a virtual connection between a destination and a source. IP by itself is something like the postal system. It allows you to address a package and drop it in the system, but there's no direct link between you and the recipient. TCP/IP, on the other hand, establishes a connection between two hosts so that they can send messages back and forth for a period of time. (See TCP).

ISP:
Internet Service Provider. A company that provides access to the Internet.

Key:
A password or a group of passwords or code used in encryption. Expressed as 128 bit or 256 bit.

• 128 bit: Since each bit can be either a "0" or a "1", then a 128 Bit encryption is equal to 2¹²⁸, or: 340 trillion, trillion, trillion codes!
• 256 bit: This is equal to 2²⁵⁶ codes!

LAN:
Local-Area Network. A computer network that spans a relatively small area. Most LANs are confined to a single building or group of buildings. However, one LAN can be connected to other LANs over any distance via telephone lines and radio waves. A system of LANs connected in this way is called a wide-area network It began in the 1970s. (See WAN).

Markup:
Markup is anything added to the content of a document that describes the text. It define the layout of the document.

Markup Language:
A language that has code for indicating layout and styling (such as boldface, italics, paragraphs, placement of graphics, etc.) within a text file. Widely used markup languages include SGML (Standard General Markup Language) and HTML (Hypertext Markup Language.

META:
In computer science, a common prefix that means "about". So, for example, metadata is data that describes other data (data about data). A metalanguage is a language used to describe other languages. A metafile is a file that contains other files. The HTML META tag is used to describe the contents of a Web page.

MIME:
Multipurpose Internet Mail Extensions. A specification for formatting non-ASCII messages so that they can be sent over the Internet, such as GIF Graphics or Postscript Files. It is also possible to define your own MIME types.

MODEM:
Modulator-Demodulator. A modem is a device or program that enables a computer to transmit data over, for example, telephone or cable lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms.

NTFS
New Technology Filing System. One of the file systems for the Windows NT operating system (Windows NT also supports the FAT file system). NTFS has features to improve reliability, such as transaction logs to help recover from disk failures.

Objects:
Portions of software coding that have characteristics such as state (a dog has fur) and behaviour (a dog barks). With OOP the state is called the field and the behaviour is called the method. Once an object is created, it can be used repeatedly in the program, just by referring to it in different ways.

OLE:
Object Linking and Embedding. Precursor to COM/ActiveX.

OOP:
Object-Oriented Programming (OOP). It's organised around "objects" rather than "actions," data rather than logic. A class of programming languages and techniques based on the concept of an “object” which is a data structure encapsulated with a set of routines which operate on the data. C++ and Java are object oriented programs. (See Objects).

Operating System:
The most important program in your computer. It runs all your hardware: keyboard, printer, monitor, disk drive, and mouse. It also keeps track of files and directories on your disk. Two types of operating systems are:

• Open Source: A program in which the source code is available to the general public for use and/or modification from its original design free of charge, i.e., open. Open source code is typically created as a collaborative effort in which programmers improve upon the code and share the changes within the community. Example: Linux, developed mainly by Linus Torvalds, works with the Apache Web server.
• Proprietary: A privately owned operating system, the code content of which is kept secret. Example: Microsoft.

PHP:
PHP: Hypertext Preprocessor. A self-referential definition - a server-side embedded scripting language used to create dynamic Web pages. "Embedded" means it's embedded within HTML tags themselves. This allows the author to move between HTML and PHP. PHP can do anything that CGI can do, BUT PHP is compatible with many databases. Created in 1994 by Rasmus Lerdorf, the advantage is that because PHP is executed on the server, surfers cannot view your PHP code!

Ping:
A utility to determine whether a specific IP address is accessible. It works by sending a packet to the specified address and waiting for a reply. PING is used primarily to troubleshoot Internet connections.

POP:
Post Office Protocol. A protocol used to retrieve e-mail from a mail server. POP2 became a standard in the mid-80's and requires SMTP to send messages. The newer version, POP3, can be used with or without SMTP.

Port:
A place where information goes into and out of a computer.

• Parallel Port: Uses a 25-pin connector and is used to connect printers, computers and other devices that need relatively high bandwidth.
• Serial Port: A port that can be used for serial communication, in which only 1 bit is transmitted at a time. A serial port is a general-purpose interface that can be used for almost any type of device, including modems, mice, and printers (although most printers are connected to a parallel port).

RAM:
Random Access Memory. The memory available to programs (applications as they're being used). RAM deletes its contents when the computer is turned off.

RDF:
Resource Description Framework. RDF is a general framework for describing a Web site's metadata, or the information about the information on the site. It allow developers to build search engines that rely on the metadata and to allow Internet users to share Web site information more readily.

Registry:
A database used by the Windows operating system to store configuration (how your computer is set up and run) information. Like DOS, it's best to stay out of the registry unless you really, Really, REALLY know what you're doing.

ROM:
Read Only Memory. Special memory used to store programs that boot the computer and perform diagnostics. ROM retains its contents even when the computer is turned off.

RSS
Depending on the source, it is short for "RDF (See) Site Summary" or "Rich Site Summary" or "Really Simple Syndication". A format for syndicating Web content. A Web site that wants to allow other sites to publish some of its content creates an RSS document and registers the document with an RSS publisher.

SGML:
Standard Generalized Markup Language. A system for organizing and tagging elements of a document. SGML was developed and standardized by the International Organization for Standards (ISO) in 1986. SGML itself does not specify any particular formatting; rather, it specifies the rules for tagging elements. These tags can then be interpreted to format elements in different ways. SGML is used widely to manage large documents that are subject to frequent revisions and need to be printed in different formats. Because it is a large and complex system, it is not yet widely used on personal computers.

SHTML:
Static HTML. Web content that stays the same where ever or when ever it's read.

Signature:
A digital system of personal identification.

SMTP:
Simple Mail Transfer Protocol. A protocol for sending e-mail messages between servers.

SOAP:
Simple Object Access Protocol. A lightweight XML-based messaging protocol used to encode the information in Web service request and response messages before sending them over a network. SOAP messages are independent of any operating system or protocol and may be transported using a variety of Internet protocols, including SMTP, MIME, and HTTP.

TCP:
Transmission Control Protocol. One of the main protocols in TCP/IP networks. Whereas the IP protocol deals only with packets, TCP enables two hosts to establish a connection and exchange streams of data. (See IP).

UNICODE:
A standard for representing characters as integers. Unlike ASCII, which uses 7 bits for each character, Unicode uses 16 bits, which means that it can represent more than 65,000 unique characters.

USB:
Universal Serial Bus. An external bus standard that supports data transfer rates of 12 Mbps. USB 2.0 is an external bus that supports data rates up to 480Mbps.

URL:
Abbreviation of Uniform Resource Locator, the global address of documents and other resources on the World Wide Web. The first part of the address indicates what protocol to use, and the second part specifies the IP address or the domain name where the resource is located. For instance:

• ftp://www.mydomain.com/stuff.exe (specifies an executable file that should be found and displayed using the ftp protocol).
• http://www.mydomain.com/index.html (specifes a web page that should be found and displayed using the http protocol).

VRML:
Virtual Reality Markup Language. A computer language that provides a three-dimensional environment for traditional Internet browsers, resulting in a simple form of virtual reality available over the Internet.

WAN:
Wide-Area Network. A computer network that spans a relatively large geographical area. Typically, a WAN consists of two or more local-area networks. (See LAN).

Webmasters:
An individual who manages a Web site.

Wiki:
A website or similar online resource which allows users to add, edit, or remove content collectively, even without registering first. The first wiki was created by Ward Cunnigham in 1995. The term wiki refers to either the Web site or the software used to create the site. "Wiki wiki" means “quick” in Hawaiian.

X.509:
A widely used standard for defining digital certificates. X.509 (Version 1) was first issued in 1988.

XHTML:
Extensible Hypertext Markup Language. A hybrid between HTML and XML specifically designed for Net device displays. XHTML is a markup language written in XML; therefore, it is an XML application. XHTML markup must conform to the markup standards defined in a HTML DTD.

XML:
Extensible Markup Language. A specification developed by the W3C. XML is a pared-down version of SGML, designed especially for Web documents. It allows designers to create their own customized tags.

ZIP:
A data compression format. Files compressed and transferred with the ZIP format are called ZIP files and have the .zip Extension.

* Many definitions courtesy of Webopedia and Wikipedia.