RJ stands for Registered Jack, a family of connectors that includes well-known variants such as RJ11, RJ12, RJ21, RJ22, and RJ50. The number 45 represents RJ45's unique designation within this family, and all Ethernet ports are referred to as RJ45.

RJ11 is typically used for telephone line connections, while RJ25 primarily connects handsets and microphones. Additionally, RJ50 is a 10-pin connector. RJ45 features 8 contacts for signal transmission, also known as 8P8C.

The RJ45 connector consists of a plug (crimped connector) and a socket (module). The plug features eight recesses and eight contacts, while the socket corresponds with eight metal pin sockets. This 8-pin modular design adheres to the EIA/TIA 568 standard, achieving electrical connections through physical contact between the metal contacts and twisted-pair cables.
RJ45 connectors are commonly used to connect Ethernet protocol devices such as servers, routers, modems, smart TVs, and game consoles to PCs.