Coaxial cables have two cylindrical conductors with a common axis that are separated by a dielectric. A dielectric is a material or medium between two conductors which can sustain an electrical field and does not conduct electricity. The most common example of a dielectric is air and the most common example of a dielectric material used in coaxial cable is polyethylene. The braid shield is used as a signal return. Coaxial cables are used for radio frequency signal transmission and video applications including HDTV and cable TV.