The favicon is the icon that shows up in the tab on any browser, such as Internet Explorer and Google Chrome. It is best advised to include a custom favicon that relates to you wiki's subject.
How to make one?
You can make one in photo programs offline and online.
How do I add one?
Go to Special:AdminDashboard and click on Theme Designer. Additionally, you can also go straight to Special:ThemeDesigner with typing the name in after the wiki's url. Go to the last tab of the page.
What are the requirements?
The favicon must be a legitimate .ico (or a .png/.jpg file converted to .ico) file that is 16 by 16 pixels in size.