If you are interested and you search the net you will find a lots definitions. But i will try to list the best of them in this article.

1.screen saver is some type of a moving picture that comes out on your screen if you haven't moved your mouse or didn't press any key for a period of time that you can set. Screen savers keep screen damage that is caused when the same areas of light and dark are displayed for long periods of time.

2.A screen saver is a program that activates after a certain amount of time has passed with no keyboard or mouse state and blanks the screen or display moving several objects across the screen; these are used to keep your screen from getting burn in.

3. You can also call it an animated picture that you can program trough the display control panel. It will appear on the screen of your computer after a time that you can program has elapsed. The most important task of the screen saver is to reduce wear and the CRT that can receive damage if the same window is left for a long period of time.