Why Baud is simply the unit for symbol rate: one baud equals one symbol (one signaling state change) per second. So symbol rate and baud rate are two names for the same quantity. Note this is not the same as bit rate, since a single symbol can carry several bits when multi-level modulation such as QPSK or QAM is used.
Watch out The choices offering a factor of two are confusing baud with bit rate; with QPSK, for example, the bit rate is twice the baud rate because each symbol carries 2 bits, but the baud rate itself never changes definition.
Baud = symbols per second, always. Bits per second is what varies with the code.