The signaling rate, or rate of state transitions, on a communications medium. One baud corresponds to one transition per second. It is often confused with the data transmission rate, measured in bits per second. Numerically, it is the reciprocal of the length (in seconds) of the shortest element in a signaling code. For very low-speed modems (up to 1200 bit/s) the baud rate and bit rate are usually identical. For example, at 9600 baud, each bit has a duration of 1/9600 seconds, or about 0.104 milliseconds.
"Some people think that baud and bits per second are equal. For example, they'll say a 28,800 bps modem transmits at 28,800 baud, and act like they know everything. But the fact is, most modems transmit multiple bits of data per baud, so while the the two values are related, they are typically not equal. So the next time your friend says his 56K v.90 modem can transfer data at 56,000 baud, you can kindly tell him that he is incorrect and explain to him the difference between baud and bps. "