A favicon is a little icon visible on the web browser tab, just before the page title. It is generally a logo with the smaller size.
The size of a favicon is 16x16 since it also gets displayed next to the URL of your site in a browser's address bar. It is visible on a users list of bookmarks and easily helps in recognizing the website from a list of websites.
Here’s how you can spot the Favicon,
The preferred format for Favicon icon is .ico. Under, favicon generator tools, if you will upload the image for Favicon in PNG, JPG, or GIF file format, it automatically converts it to the ICO format.