A plug-in is a separate application program that enhances and adds capabilities to your Web browser so that it is able to interact with multimedia on the Web.

Plug-ins make it possible to listen to streaming audio and to watch streaming video. They also provide Internet telephone which allows you to speak with other people over the Web.

Plug-ins can display documents with the quality of desktop publishing. You can also explore three-dimensional multimedia environments.

In short, plug-ins allow you to access the new technologies on different Web pages.