The UART standard

Standard EIA RS-232-C, Electronic Industries Alliance
First released in 1969, then updated.

It is a synchronous serial protocol

Features
A single transmit wire, at the following bps rates:
Obsolete: 300, 600, 1200, 2400, 4800
Common: 9600, 19200, 38400, 57600, 115200
Rare: 230400, 460800
Common (on-pcb): 1000000, 2000000, 4000000
One 'start' bit and one or two 'stop' bits (usually 1)
Optinal parity bit - rarely used
So every byte is 10 bits long

The associated logic block is called UART, sometimes USART
UART: Universal Asyncronous Receiver/Transmitter
USART: Universal Synchronous/Asyncronous Receiver/Transmitter