The full name of RJ is Registered Jack, which means registered jacks, the source of which is the code in Bell System's Universal Service Ordering Codes (USOC). Universal Service Ordering Codes is a series of registered jacks developed by Bell Systems and their wiring. The function is to connect the user's equipment to the public network.
The RJ45 is a type of information socket (ie, communication terminal) connector in the wiring system. The connector consists of a plug (connector, crystal head) and a socket (module). The plug has 8 grooves and 8 contacts. RJ is the abbreviation of Registered Jack, which means "registered socket." In the FCC (Federal Communications Commission Standards and Regulations), RJ is the interface that describes the public telecommunications network. The RJ45 of the computer network is a common name for the standard 8-bit modular interface.