The process of running a part or piece of equipment for a period of time to make sure it is functioning correctly. This is normally done just after manufacturing or after some major repair work has been done. The specific purpose of burning in new items is to address infantile failure problems, which is the known statistical fact that electronic equipment is most prone to fail within the first 24 to 48 hours of use. Quite often the failures are triggered by heat when the unit comes up to operating temperature. For this reason many devices are subjected to extremes of heat and/or cold during the burn-in phase.
Burn in also describes what can happen to older CRT screens when the same image is shown on them for long periods of time. An impression of the image is burnt into the screen, permanently damaging it. Thus, screensavers were created.