CAT5 is an Ethernet cable standard defined by the Electronic Industries Association and Telecommunications Industry Association (commonly known as EIA/TIA). CAT5 is the 5th generation of twisted pair Ethernet cabling and the most popular of all twisted pair cables in use today.

CAT5 cable contains four pairs of copper wire. CAT5 supports Fast (100 Mbps) Ethernet and comparable alternatives such as ATM. As with all other types of twisted pair EIA/TIA cabling, CAT5 cable runs are limited to a maximum recommended run rate of 100m (328 feet). CAT5 enhanced (CAT5e), supports short-run Gigabit Ethernet (1000 Mbps) networking by utilizing all four wire pairs and is backward-compatible with ordinary CAT5.

Twisted pair cable like CAT5 comes in two main varieties, solid and stranded. Solid CAT5 cable supports longer runs and works best in fixed wiring configurations like office buildings. Stranded CAT5 cable, on the other hand, is more pliable and better suited for shorter-distance, movable cabling such as on-the-fly "patch" cabling.

Though newer cable technologies like CAT6 and CAT7 are being developed, CAT5 cable remains the popular choice, because it is both affordable and plenty fast enough for today's LANs.