Category 4 cable (Cat 4) is a cable that consists of four unshielded twisted-pair (UTP) copper wires with a data rate of 16 Mbit/s and performance of up to 20 MHz.
It is used in telephone networks which can transmit voice and data up to 16 Mbit/s.
For a brief period it was used for some token ring, 10BASE-T, and 100BASE-T4 networks, but was quickly superseded by Category 5 cable. It is no longer common or used in new installations. Category 4 cable is not recognized by the current version of the TIA/EIA-568 data cabling standards.
References
Category 4 cable Wikipedia(Text) CC BY-SA