screen saver

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A software program that displays constantly changing images or dims the brightness of a display screen to protect the screen from having an image etched onto its surface.

Wiktionary

1. n. alternative spelling of screensaver.

WordNet 3.0

1. n. (computer science) a moving design that appears on a computer screen when there has been no input for a specified period of time