Baud is a term related to the speed of a modem. Specifically it's the amount of bits a modem can send or receive per second. Instead of baud most user say the "baud rate" a modem has. The baud rate is measured in the number of times per second that the carrier signal shifts value, however these days you are more than likely to see modem speeds measured in bps "bits per second" rather than in baud.