The transmission speed (or rate) of a modem. Named for French telegrapher Emile Baudot, who developed a five-level telegraph code. Baud rate is roughly one half dot cycle per second in Morse code, one bit per second in binary signals, or other values depending on the coding system used. Note that baud rate is not the same thing as bit rate, although the two are often used interchangeably – with a modem, its baud rate can be quite different from its bit rate.
You’ll often see MIDI specified as 31.25 KBaud. Technically, this is not correct. The spec should actually be a bit rate of 31,250 bits per second.