An imagemap is a clickable image where different areas of the image links to different web addresses. I.e. you can link to multiple addresses by dividing the image into several areas. If you have an image of the organizational scheme and want to link to the departments for example.
A tip for accessibility! For increased accessibility you can provide text as an alternative to image maps. SiteVision is using client based imagemaps.
Describe the object with an alt-text.
Describe each link in the object with a title-text.