bandwidth is the available frequency range for communication over a channel. It is the difference of the upper frequency(max of the range) and lower frequency(min of the range). its unit is Hertz. it indicates capacity of the channel. it is also sometimes expressed in bits per second,like bitrate. bandwidth depends upon baudrate(signal rate). it is an attribute of channel.
bitrate is the number of bits send per second. its unit is bps(bits per second). it is an attribute of transmission. bitrate is dependant on available bandwidth and also the line coding scheme