screen saver

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Alternative spelling of screensaver.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

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