The bit rate is the number of bits occurring or transferred per unit of time. The bitrate is usually expressed in bits per second (bit/s). Note that the transmission speed of units of data is sometimes referred to as the number of bytes per seconds (B/s).
Prefixes are used for high bitrates. The binary prefixes have the following meaning:
The bitrate does not necessarily have to be constant (CBR: Constant bitrate). Especially video, audio or speech coding can result in a variable bitrate (VBR). A special form of VBR is average bitrate (ABR) in which the encoder tries to maintain a specific (average) bitrate. ABR can also be seen as the average bit rate of a vbr encoded bitstream.