Bit rate is a measure of the number of data bits (that's 0's and 1's) transmitted in one second. A figure of 2400 bits per second means 2400 zeros or ones can be transmitted in one second, hence the abbreviation 'bps'. Baud rate by definition means the number of times a signal in a communications channel changes state.It may vary.like in Manchester encoding and differential Manchester encoding baud rate= 2*bit rate.
Baud rate is mostly used in telecommunication and electronics, representing symbol per second or pulses per second, whereas bit rate is simply bit per second. To be simple, the major difference is that symbol may contain more than 1 bit, say n bits, which makes baud rate n times smaller than bit rate.
Suppose a situation where we need to represent a serial-communication signal, we will use 8-bit as one symbol to represent the info. If the symbol rate is 4800 baud, then that translates into an overall bit rate of 38400 bits/s. This could also be true for wireless communication area where you will need multiple bits for purpose of modulation to achieve broadband transmission, instead of simple baseline transmission.