This plug-in lets you select areas in an image. These areas will be linked to a text, an image, a script, an Internet site... which will appear by clicking on these areas. A HTML file is created, you can view in a Web browser.

This is a complex tool which has never been completely described (Probably because Web page makers offer this function). You can find a good introduction in Grokking the GIMP .

You can find this filter through Filters → Web → ImageMap