Baud is a unit of signaling speed. The speed in bauds is the number of discrete changes per second in some aspect of a signal (e.g., voltage in a wire). Transmission speeds are now more commonly measured bits per second (bps), rather than bauds. The two terms were roughly synonymous until modems began to exceed 2,400 bps, after which they diverged more widely as modem speed has increased. Modems now use coding techniques to transmit more than one bit per baud, making their true baud ratings irrelevant.
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