Windows Phone 7 features a user interface based on a design system codenamed and commonly referred to as Metro. The home screen, called "Start screen", is made up of "Live Tiles". Tiles are links to applications, features, functions, and individual items (such as contacts, web pages, applications, or media items). Users can add, rearrange, or remove tiles. Tiles are dynamic and update in real-time – for example, the tile for an email account would display the number of unread messages or a tile could display a live update of the weather.