A plugin is a software component that adds a specific feature to an existing computer program). It is a piece of software that adds new features or extends functionality on an existing application. Plugins are also known as add-ons, add-ins, add-ons, or addons). They are commonly used on websites that are built with content management systems. Plugins can be used to customize programs and software without affecting the source code. They are designed to "plug in" to existing operational frameworks, allowing users to get the features they want.

Plugins can be used to add specific features to applications and software without affecting the source code. For example, a video game console emulator may use plugins to modularize the separate subsystems of the devices they seek to emulate). Graphics software use plugins to support file formats and process images). A Photoshop plugin may do this). In web browsers, plugins are used to extend the capabilities of the browser. For example, Adobe Acrobat, Adobe Flash, Java, QuickTime, RealPlayer, Shockwave, Silverlight, VRML (Virtual Reality Modeling Language), and X3D are examples of browser plugins.

Plugins depend on the services provided by the host application and do not usually work by themselves). The host application provides services which the plugin can use, including a way for plugins to register themselves with the host application and a protocol for the exchange of data with plugins). Programs may also implement plugins by loading a directory of simple script files written in a scripting language like Python or Lua).

Plugins are invaluable tools for webmasters and site visitors alike. They can add entirely new dimensions to a website, improving its functionality and user experience. However, when a website owner downloads and installs a plugin, they are at the mercy of the third-party developer that created the program. Some plugins are top-notch and function exactly as described, while others are buggy, out of date, or lack security.