Does a screensaver save the computer display screen?
And if it does, what does it save the screen from?
If the above two questions have a NO answer, than why is it called screensaver?
This is a summary of Wikipedia:Screen burn-in.
CRT, Plasma, and OLED displays
These displays develop burn-in due to degradation of the light emitting compounds. Screensavers were initially designed to prevent phosphor burn-in in cathode ray tube (CRT) monitors. Plasma displays are also susceptible to burn-in due to overheating of the phosphors. Organic light-emitting diode (OLED) displays develop burn-in due to degradation of the organic compounds. (cnet)
In the worst cases, the burn-in is visible even when the display is not powered:
Liquid crystal displays (LCDs) can suffer a different type of burn-in (gizmodo) also referred to as image persistence (fujitsu). Liquid crystals are designed to allow light through in their relaxed state, but can become "stuck" at a particular level of activation, causing an effect that looks very similar to traditional burn-in. (ref)
Screensavers can be useful in preventing burn-in on CRT, plasma, and OLED displays. For LCD displays, image persitence can be prevented by using a screensaver. (fujitsu)