Plug-in

In, a plug-in (or plugin, add-in, addin, add-on, or addon) is a that adds a specific feature to an existing. When a program supports plug-ins, it enables customization.

History
Digital Darkroom from Silicon Beach Software 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".

s historically allowed s as plug-ins, such as Macromedia Flash Player to play back Flash content and for s, though they have now been mostly  due to concerns of internet security.