A transient screen is a pop-up screen such as a notification or dialog screen on a mobile phone

Mobile phone

A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...

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It covers only part of the screen as well as dimming the remaining area. It helps to give the user a potentially high priority message, such as a new text message, voice mail or incoming phone call, either when the user gives the phone their attention, for example, by opening a flip phone or when running an application such as a game

Game

A game is structured playing, usually undertaken for enjoyment and sometimes used as an educational tool. Games are distinct from work, which is usually carried out for remuneration, and from art, which is more often an expression of aesthetic or ideological elements...

in the foreground.