Favicon
It is used by webbrowsers in address bar(URL).It helps to identify our site visually. In mobile, it is used as application icon.
Favicon means Favourite Icon. It is 16 * 16 pixel image. By default wordpress have a favicon. But we can change it to our icon.
Navigate to wordpress dashboard(As admin)=>Appearance=>Customize
On the left side bar, Click on Site Identity=>Select Site Icon .Select the favourite icon.
New favicon will be displayed in the browser on the left side of the title.
Reference : Create a Favicon – WordPress.org Documentation