Software component that adds a specific feature to an existing computer program.

When a program supports plugins, it enables customization. The common examples are the plugins used in web browsers to add new features such as search-engines, virus scanners, or the ability to use a new file type such as a new video format. Well-known browser plugins include the Adobe Flash Player, the QuickTime Player, and the Java plugin, which can launch a user-activated Java applet on a web page to its execution on a local Java virtual machine.