100BASE-T is any of several Fast Ethernet 100 Mbit/s CSMA/CD standards for twisted pair cables, including: 100BASE-TX (100 Mbit/s over two-pair Cat5 or better cable), 100BASE-T4 (100 Mbit/s over four-pair Cat3 or better cable, defunct), 100BASE-T2 (100 Mbit/s over two-pair Cat3 or better cable, also defunct). All are or were standards under IEEE 802.3.
The vast majority of common implementations or installations of 100BASE-T are done with 100BASE-TX.
