Also known as an extension, add-on and add-in, a plugin is software which adds a feature to an existing computer program.
Allowing for customisation and added functionality, popular plugins include Adobe Flash Player and the QuickTime Player. Today, most people come into contact with plugins via their web browser, with plugins allowing features like search engines and virus scanners to be added to their browser.
How can a plugin help you?
There are multiple reasons as to why an application supports plugins – this could range from adding new features and reducing the size of the application, to enabling third-party developers to create features which extend the application. Web browsers, for example, use plugins like Java SE to expand functionality, while packet sniffers use plugins like OmniPeek to decode packet formats.
Plugins first appeared in the mid-1970s, when the EDT text editor running on the Unisys VS/9 OS allowed a program from the editor access the editor buffer. This allowed an external program to access an edit session in memory.