What:
A favicon is an icon associated with a particular website. You typically see it displayed in a browser's address bar near the URL, next to the page's name / title on a browser tab or in the bookmark menu, and while dragging and dropping a link anywhere in the user interface.
A favicon is otherwise known as a website icon, shortcut icon, url icon, or bookmark icon.
Benefits:
Branding: A good way to personalize or brand your site.
Professional-looking: Gives it kind of a finished and professional feel.
Usability: Makes it easier for the user to find your site in a list of bookmarks or from amongst multiple browser tabs.