A cable is made of many wires or optical fibers twisted together to make a larger wire. Each of these wires may be covered. Some cables contain both electrical wires and optical fibers. There are many kinds of cables, including coaxial cables which block out radio or magnetic interference from other wires or cables, by having one wire inside an insulated tube surrounded by a second wire, acting as a metal tube along the same axis. Wire ropes are a common type of cable.
Electrical cables are usually made of copper, because electricity moves well through copper, but it is not as expensive as silver or other better conductors. Cables are sometimes made of aluminium because it is cheaper than copper.