extension(1) An extra feature added to a standard programming language or system.
(2) In DOS and some other operating systems, one or several letters at the end of a filename. Filename extensions usually follow a period (dot) and indicate the type of information stored in the file. For example, in the filename EDIT.COM, the extension is COM, which indicates that the file is a command file. (Depending on the operating system, the punctuation separating the extension from the rest of the filename may or may not be considered part of the extension itself.)
(3) In Macintosh environments, a program that extends the system's capabilities. When they reside in the Extensions folder, extensions are loaded into memory when the system starts. On older Macs (System 6 and earlier), extensions were called inits.
(4) Same as plug-in.
Stay up to date on the latest developments in Internet terminology with a free weekly newsletter from Webopedia. Join to subscribe now.
Webopedia's student apps roundup will help you to better organize your class schedule and stay on top of assignments and homework. Read More »List of Free Shorten URL Services
A URL shortener is a way to make a long Web address shorter. Try this list of free services. Read More »Top 10 Tech Terms of 2015
The most popular Webopedia definitions of 2015. Read More »
Java is a high-level programming language. This guide describes the basics of Java, providing an overview of syntax, variables, data types and... Read More »Java Basics, Part 2
This second Study Guide describes the basics of Java, providing an overview of operators, modifiers and control Structures. Read More »The 7 Layers of the OSI Model
The Open System Interconnection (OSI) model defines a networking framework to implement protocols in seven layers. Use this handy guide to compare... Read More »