Like 10BaseT but 10x faster, giving you 100mbit.
Like 10BaseT this uses a star configuration, where each client node (computer) connects to a central hub with one cable, and that cable cannot exceed 100m in length. As such, damage to any one cable only affects that computer - the rest of the LAN is still operational.
While talking about star topology, its worth noting that both 10BaseT and 100BaseT over an unswitched network might present a star topology physically, they are actually a bus topology as far as ethernet is concerned - all traffic is rebroadcast to all other nodes. If they are used in a SwitchedEthernet? then they are a star topology.
100BaseT can either be run over Category 3 UTP cable by using all four pairs, or much more commonly over Category 5 cable, only using two pairs. (The infamous "Cat-5").
100BaseT like 10BaseT will run in Full Duplex (when either found in auto setting or hard set) when connected back-to-back (when using a full MDI to MDI-X cross-over cable) or connected to a switch port.
100BaseTX requires a minimum of a Category 5 Cable installed as it uses two pairs, one pair for Transmit, and one pair for receive. 100BaseT4 requires a minimum of Category 3 Cable installed as it use four pairs. two pairs for trasmit, and two pairs for receive.