Favicon Example

Favicon is short for "favorite icon."
Most "modern" browsers will display a favicon in the browser's tab for the page.
Most browsers will also display the favicon with a bookmark you make for the page.
But browser support is not completely uniform as you can see in the favicon wiki page if you are curious.

The reason browser support isn't more uniform is that favicons are NOT part of the official HTML standard mainained by the W3C.
For example, most browsers display favicons in the browser tabs and bookmarks, but Safari typically doesn't (for whatever reason) although Safari used to show them.