It is often used in structured cabling for computer networks such as fast Ethernet, although it is often used to carry many other signals such as basic voice services, token ring, and ATM (at up to 155 Mbits/s, over short distances).
The other well known flavour of this type of cable is the 10 Mbit/s Category 3 cable. Less well known is the 20 Mbit/s Cat 4. Cat 4 offered only a small advance in speed over Cat3, and was generally ignored in favour of Cat 5. Cat 1 and Cat 2 are 1 Mbit/s systems for voice and low-speed data.
Patch leads created from cat-5 are often terminated with RJ45 electrical connectors. Normal Cat 5 cables are wired "straight through" and connect a computer to a hub. In other words, pin 1 is connected to pin 1, pin 2 to pin 2, etc. The RJ-45 pinout for a Cat 5 cable can either be TIA-568A or TIA-568B. TIA-568A is used by some phone systems and Token Ring. Most everything else, such as the Ethernet standards 10BASE-T and 100BASE-TX, use TIA-568B.
In Ethernet, "crossover" Cat-5 cables are used to connect two hubs together, in which pairs two and three are reversed. Crossover cables can also be used to connect two PC's NICs directly (with no intervening hub). See the TIA-568B article for a pinout diagram.
Cat 5e cable is an enhanced version of Cat 5 for use with 1000 Base-T networks, or for long-distance 100 Base-T links (350 m, compared with 100 m for Cat5). It must meet the EIA/TIA 568A-5 specification.
Cat 6 cable is defined by the ANSI TIA/EIA 568B-2.1. It is suitable for 1000 Base-T (gigabit) Ethernet up to 100 m.