A favicon is that little icon that appears in the left-hand side of the address bar of your browser when you visit a website, or in your bookmarks menu if you bookmark it, or on the tab if you are using a browser with tabs. Creating a good favicon is an important part of developing a website, since that icon is the most frequently-visible representation of your website. If you design it right, just seeing it will make your site pop into someone's mind when they open their bookmarks. If you get it wrong, or don't bother with it at all, you've missed an opportunity to make your site stand out just a little bit more.