RG-6/U is a common type of coaxial cable used in a wide variety of residential and commercial applications. The term "RG-6" itself is quite generic and refers to a wide variety of cable designs, which differ from one another in shielding characteristics, center conductor composition, and dielectric type. RG-6 was originally a military spec where RG means Radio Guide, but is now obsolete; in practice, the term "RG-6" is generally used to refer to coaxial cables with an 18 AWG center conductor and 75 ohm characteristic impedance.