Coaxial cable, or
coax (pronounced ), is a type of
cable that has an inner conductor surrounded by a tubular insulating layer, surrounded by a tubular conducting shield. Many coaxial cables also have an insulating outer sheath or jacket. The term
coaxial comes from the inner conductor and the outer shield sharing a geometric axis. Coaxial cable was invented by English engineer and mathematician
Oliver Heaviside, who patented the design in 1880. Coaxial cable differs from other
shielded cable used for carrying lower-frequency signals, in that the dimensions of the cable are controlled to give a precise, constant conductor spacing, which is needed for it to function efficiently as a
transmission line.