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.)

Also see Data Formats and Their File Extensions in the Quick Reference section of Webopedia.

(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.

Webopedia Staff
Webopedia Staff
Since 1995, more than 100 tech experts and researchers have kept Webopedia’s definitions, articles, and study guides up to date. For more information on current editorial staff, please visit our About page.

Related Articles

Human Resources Management System

A Human Resources Management System (HRMS) is a software application that supports many functions of a company's Human Resources department, including benefits administration, payroll,...

How To Defend Yourself Against Identity Theft

Almost every worldwide government agency responsible for identity theft issues will tell you the same thing: The first step to fighting identity theft is...

Infographic

An infographic is a visual representation of information or data. It combines the words information and graphic and includes a collection of imagery, charts,...

Phishing

What is phishing? Phishing is a type of cybercrime in which victims are contacted by email, telephone, or text message by an attacker posing as...

ScalaHosting

ScalaHosting is a leading managed hosting provider that offers secure, scalable, and affordable...

HRIS

Human resources information system (HRIS) solutions help businesses manage multiple facets of their...

Best Managed Service Providers...

In today's business world, managed services are more critical than ever. They can...