APC------- UPS

UPS = uninterruptible power supply. It's a unit that provides surge protection, smooths out variations in the power supply, etc. It's 'uninterruptible' because it includes battery power to keep the computer running in a power failure. You usually can't run the computer for a long time, but the battery gives you time to close out docs and apps and do an orderly shutdown, rather than having the power drop out. APC = American Power Conversion, of the main makers of UPS equipment.