screensaver

A screensaver is software that controls a monitor of the host computer with the intent of preventing screen burn-in for a screen susceptible to it. Generally, a screensaver starts controlling a monitor when the computer has been idle for a designated period of time and fills the screen either with black or with changing graphics that tend to prevent each pixel from being on for a long time. Although monitors were commonly constructed with screen technology that was susceptible to burn-in, most modern monitors are LCD which are not. Notably, another modern technology, OLED, is susceptible. Read more on Wikipedia