A screen saver, which serves as a desktop enhancement like a wallpaper, is a great way to personalize your computer. It can also be an animated image activated on a computer display when no user activity has been perceived for a while. Its purpose is to prevent burn-in—the burning of image into the phosphor inside the cathode ray tube (CRT) after hours of the same image being rescanned. With the efficiency of today’s technology, however, CRT burn-in is quite unlikely in our modern computers.
Windows and Mac come in with built-in screen savers, or at least lets you set up one from a choice of many. Whenever you leave your computer unattended for a couple of minutes, the screensaver is activated on the screen or computer display. On your iphone, it would be helpful to have a screen saver enabled, though, many prefer simply a black screen to save on battery life.