A UPS is an uninterruptible power supply. In other words, it can power your computer, monitor, peripherals, server, or other equipment in the event of a power outage. In this way, the device gives you the opportunity to react (save valuable information, turn off your computer, turn on the backup power (aggregate) and others).
Usually, the UPS consists of one or more batteries, which, when the power supply is interrupted, supply current to the consumers connected to them.