A set of four bits. Some line coding techniques encode blocks of 4 bits of data at a time, rather than 1 or 2 bits.The 4B/5B technique, for example, encodes a 4-bit block of data into a 5-bit block of signal in order to provide sufficient clocking pulses and signal transitions to synchronize the network and to provide some level of error detection. 4B/5B is used in 100Base-TX, 100Base-FX, and Fiber Distributed Data Interface (FDDI) LANs. Compare to nibble. See also 4B/5B, line coding, and synchronization.