plug-in

In computing, small add-on file which enhances the operation of an application program, often by enabling it to launch, display, or interpret a file created using another one. The first plug-ins were made for graphics programs in the 1980s, but the practice became very popular in the mid-1990s, when a range of plug-ins became available to enhance the multimedia capabilities of Netscape's Navigator browser. Plug-ins are often created and distributed by independent developers rather than the manufacturer of the program they extend.