RJ45 refers to a physical connector standardized as IEC 60603-7 8P8C modular connector with eight conductors. Although these connectors were originally used as telephone connectors, they are not used as computer networking connectors. Check out the details on www.ebay.com/gds/What-is-RJ45/10000000021227408/g.html.
Short for Registered Jack-45, an eight-wire connector used commonly to connect computers onto a local-area networks (LAN), especially Ethernets. RJ-45.A connector utilized in 10BaseT and 100BaseTX networks with UTP cabling.