It's a small image file that appears to the left of the URL in the address bar of your browser. You can take a small 16 x 16 or 32 x 32 gif or jpg image and rename it to favicon.ico then place it in your forum home. You can also add some code to your headinclude template to make it show. Search this site for "favicon" and you'll find several posts that tell you what that code is. The code is not necessary, just a helper.