Bit rate is a measure of bandwidth which indicates how much data is traveling from one place to another on a computer network. Bit rate is usually expressed in kilobits per second (kbps) or megabits per second (Mbps).
The bit rate of an audio or video stream indicates how much data must be transferred concurrently in order to properly receive the stream. Buffering can help mitigate variance in available bandwidth.
Note that bit rate does not describe how long is takes to get from one part of the network to another, only how many bits can be transferred concurrently. See latency for a measurement of delay.