When opening a new activity that is on top of the wallpaper when the current activity is also on top of the wallpaper, this is the animation that is run on the current activity (which is exiting the screen). The wallpaper remains static behind the animation.

Must be a reference to another resource, in the form "@[+][package:]type:name" or to a theme attribute in the form "?[package:][type:]name".

[Android Documentation]