RG-59/U is a specific type of coaxial cable, often used for low-power video and RF signal connections. The cable has a characteristic impedance of 75 ohms. The 75 ohm impedance matches a dipole antenna in free space. "RG" (for Radio Guide) was originally a unit indicator for bulk radio frequency (RF) cable in the U.S. military's Joint Electronics Type Designation System. The suffix "/U" means “for general utility use.” The number "59" was assigned sequentially. The "RG" unit indicator is no longer part of the and cable sold today under the RG-59 label does not necessarily meet military specifications.