The BNC connector (initialism of "Bayonet Neill–Concelman") is a miniature quick connect/disconnect radio frequency connector used for coaxial cable. It is designed to maintain the same characteristic impedance of the cable, with 50 ohm and 75 ohm types being made. It is usually applied for video and radio frequency connections up to about 2 GHz and up to 500 volts. The connector has a twist to lock design with two lugs in the female portion of the connector engaging a slot in the shell of the male portion. The type was introduced on military radio equipment in the 1940s and has since become widely applied in radio systems, and is a common type of video connector. Similar radio-frequency connectors differ in dimensions and attachment features, and may allow for higher voltages, higher frequencies, or three-wire connections.

The BNC connector features two bayonet lugs on the female connector; mating is fully achieved with a quarter turn of the coupling nut. It uses an outer conductor with slots and some plastic dielectric on each gender connector. This dielectric causes increasing losses at higher frequencies. Above 4 GHz, the slots may radiate signals, so the connector is usable, but not necessarily stable, up to about 11 GHz. BNC connectors are made to match the characteristic impedance of cable at either 50 ohms or 75 ohms (with other impedances such as 93 ohms for ARCNET available though less common). They are usually applied for frequencies below 4 GHz^[1] and voltages below 500 volts.^[2] The interface specifications for the BNC and many other connectors are referenced in MIL-STD-348.^[3]