An image map is a picture on a Web page that provides different links to other Web pages, depending on where a user clicks on the image. Image maps are often "real" maps, such as the example in the screenshot below from the Dell support site.
More often, image maps are pictures of navigation items such as this example from the Sun Microsystems Web site:
Here's another navigation map at the King Co., Washington, site:
Here is another interesting image map which is on the home page of the web site of the Target stores. This image (now with correct alt-text, "In the Spotlight") contains 33 clickable areas, corresponding to the text in the smallest font, like "30-Minute-Meal Recipes."