- noun a connector used in telephone systems with eight connections. A similar looking connector, often referred to as an RJ-45 connector is used to connect 10BaseT UTP cable in an Ethernet local area network.
- Abbreviation of registered jack-45. A connector that holds up to eight wires, and which utilized for the transmission of digital data over ordinary phone lines and LANs. Although jack generally refers to the connector into which a plug is inserted, RJ-45 may refer to the jack, plug, or both. Also called RJ-45 connector.