Dictionary.net

In serial communications, where each bit of the message istransmitted in sequence, stop bits are extra "1" bits whichfollow the data and any parity bit. They mark the end of aunit of transmission (normally a byte or character).For example, characters on an EIA-232 serial line may haveone or two stop bits added. Some UARTs even allow for 1.5stop bits but one is probably the most commonly used. Aserial connection may be described as, for example, "8N1"which means eight data bits, no parity and one stop bit.