An Ethernet standard that transmits at 100 Mbps. Introduced in 1995 and officially the IEEE 802.3u standard, 100Base-T is a 100 Mbps version of the 10 Mbps 10Base-T. Like 10Base-T, 100Base-T is a shared media LAN when used with a hub (all nodes share the 100 Mbps) and 100 Mbps between each pair of nodes when used with a switch. All modern Ethernet devices are 10/100/1000, supporting 10, 100 and 1000 Mbps (10Base-T, 100Base-T and 1000Base-T) See Ethernet adapter
and Gigabit Ethernet
T, TX and T4
100Base-T uses two pairs of wires in at least Category 5 UTP cable, while 100Base-TX requires two pairs in Category 6. 100Base-T4 uses all four wire pairs in older Category 3 cables. See cable categories
"Twisted Pair" Ethernet
All stations in a 100Base-T Ethernet are wired to a central hub or switch using twisted pair wires and RJ-45 connectors.
Fast Ethernet Is No Longer Fast
The moniker "Fast Ethernet" was used for 100 Mbps 100Base-T; witness this Staples product ad in 2013. Today, Gigabit Ethernet is the norm, which is 10 times faster.