Baud — a unit of measurement for symbol rate, indicating the number of changes in the informational parameter of a carrier periodic signal per second. The term is named after Emile Baudot, the inventor of the Baudot code — a character encoding system for teletypes.
Manipulation rate (symbol rate) in communications technology refers to the number of distinct signal states in a transmission line per unit of time. These states are called symbols. The primary unit of measurement for manipulation rate is the baud (number of symbols per second).
A common misconception is that baud represents the number of bits transmitted per second. In reality, this is only true for binary encoding, which is not always used. Baud rate varies across standards and depends on the encoding method. For example, in modern modems, Quadrature Amplitude Modulation (QAM) is employed, where a single change in the signal level can encode multiple bits (up to 16). For instance, with a symbol rate of 2400 baud, the data transmission rate can be 9600 bit/s because each time interval transmits 4 bits.
Additionally, baud may express the total channel capacity, including service symbols (bits), if present. The effective channel speed, however, is expressed in bits per second (bps).