A screen saver is a program or image that is displayed on a computer screen when it is not being used. Its purpose is to prevent permanent damage to the screen and reduce energy consumption. Full definition
«Reading» a story with the ears is a great screen saver for the eyes. (writerunboxed.com)
The screenplay is really just an excuse for visuals, but without a purpose behind those the visuals, they quickly become as dull as a laser show, or a computer screen saver. (chron.com)
This can be done under system preferences > desktop & screen saver > hot corners. (lawyerist.com)