plugin

n. additional software card that connects to a computer and communicates easily with the Internet and HTML files

A plugin (plug-in, addin, add-in, addon or add-on) is a computer program that interacts with a host application (a web browser or an email client, for example) to provide a certain, usually very specific, function "on demand". Applications support plugins for many reasons. Some of the main reasons include: enabling third-party developers to create capabilities to extend an application, reducing the size of an application, and separating source code from an application because of incompatible software licenses.
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