Universal Asynchronous Receiver-Transmitter. An electronic circuit contained within the communications port(s) of the computer that decodes and encodes data in the fashion required by the specific machine for receiving and transmitting purposes. The UART also performs the actual data transmission to the communication device, once it has been encoded and is ready to send.
Uninterruptible Power Supply. A battery reserve system for computer power installed to supply power in the event of outage. These systems protect against data loss during power outage.