The baud rate is defined as the number of discrete signal events per second occurring on a communications channel. Due to advanced coding methods, each signal can carry more than one bit. If e.g. 4 different signal events are defined, each signal level represents 2 bits. In that case the baud rate is only half of the bit rate. These events can be 4 different phases (4-PSK), 4 different amplitudes (4-ASK) or 4 different frequencies (4-FSK) which are used to transport 2 bits at once.
Baud rate is commonly used to mean bit rate (bps). In communications software, baud rate commonly refers to the computer's serial port rate.