Favicon refers to Favorite Icon, which is a small icon displayed in the tab’s name on the browser. Users can distinguish each tab by this icon. It often has the size is 16x16px and is saved in a file named
favicon.io in the root folder of the server. It also is considered as an abridged logo of your business.
Every website often has a favicon applied to all pages on the site. But, you may want to highlight your products by set individual favicon for each product page. Using Meta Box plugin along with editing the theme a little bit will help you get it.