Favicon (short for "favorites icon") is an icon associated with a website that displays in the browser address bar, history pages, bookmarks or favorites.
Always use the Microsoft favicon on Microsoft marketing sites, unless your site is a web client like outlook.com, where it specifically calls for the products favicon. It reinforces the Microsoft brand and strengthens visitor recognition between sites.
The Microsoft favicon file contains the Microsoft symbol in six sizes, to accommodate various resolutions. The file is available in the Resources section below.