Definition: CAT 5 is short for Category 5 cable, which is the most commonly used cable for wiring computer networks. CAT 5 cable is typically round and is found in various colors, however, the color of the sheathing is irrelevant. All CAT 5 cable features four twisted pairs of wires inside the sheathing.

CAT 5 cable is available with the wire pairs having either a solid or stranded core. The stranded core is typically used for patch cables that are used to connect the computer network card to the network jack terminus. The solid core wire is typically used for runs from the wall termination back to the network patch panel. Solid core CAT 5 cable is also available in standard sheathing or plenum.

Plenum CAT 5 is the same internally, but features a special outer sheath that puts off no toxic fumes when it burns.

zSB(3,3) Plenum CAT 5 is typically required to meet fire codes in buildings where the cable runs through an area where toxic fumes could enter the living space of a home or office during a fire.