Plug-in

A plug-in is a file containing data used to alter, enhance, or extend the operation of a parent application program.

History
from was the first Macintosh program to incorporate a plug-in architecture in 1988. Ed Bomke at Silicon Beach is credited with having coined the term "plug-in".

Plug-ins, both commercially and indepently authored, can usually be downloaded for free and are stored locally. Plug-ins can come in different versions specific to particular operating systems (such as Windows or macOS).

Web browser plug-ins
The Netscape Navigator web browser supports plug-ins which display or interpret a particular file format or protocol such as QuickTime, RealAudio, Adobe PDF, Flash Player, or Corel CMX (vector graphics). The file to be displayed is included in a web page using an EMBED HTML tag. However, such browser plug-ins and extensions have gradually fallen out of favor with the rise of malware, especially on PCs.