The data rate is a term to denote the transmission speed, or the number of bits per second transferred. The useful data rate for the user is usually less than the actual data rate transported on the network. One reason for this is that additional bits are transferred for e.g signalling, the address, the recovery of timing information at the receiver or error correction to compensate for possible transmission errors.
In telecommunications, it is common use to express the data rate in bits per seconds (bit/s), see bitrate. In datacommunication, the data rate is often expressed in bytes per second (B/s).