Uninterrupted Power Supply or UPS. is a device that provides back up battery power to IT systems and appliances. In a Hosted VoIP system, UPS devices are used locally to provide emergency power to phones during a power outage. These systems can be used for all types of electronics that are required to stay operational at all times. UPS systems vary in size from small battery packs that back up local PCs to rack-mount models that back up servers. All the way up to systems using backup generators that keep emergency lights and equipment running for building infrastructure.
Merriam-Webster Online Dictionary
UPS (abbreviation)uninterruptible power supply