RJ stands for registered jack which is a standardized physical network interface. It contains jack construction and wiring pattern for connecting telecommunications or data equipment to a service provided by local exchange carrier or long distance carrier. The standard designs for RJ45 connectors along with their wiring are named as RJ11, RJ14, RJ21, RJ48 etc. Most of these interfaces are used all around the world but some are very common in North America.
The RJ45 mainly use the physical connectors made up of the modular connector and 50 pin miniature ribbon connector types. Fro example, RJ11 uses a 6 position 4 conductor modular plug and jack while RJ21 uses a 50 pin miniature ribbon connector.
RJ45 is considered to be the standard type of connector used for the network cables. These connectors are commonly found with Ethernet cables and networks. The construction of RJ45 connector consists of 8 pins to which the wire strands of a cable are interfaced electrically. The standardized pin outs of this connector defines the arrangement of the individual wires that are needed while attaching the connectors to the cable.
There are some other types of connectors whose resemblance are similar to RJ45 and can make easily confused in differentiating them. For an example, the RJ11 connector used with the telephone cables are slightly narrower than RJ45 connector.
RJ45 connector is commonly used in telephony applications and for network cabling. In special cases, it is also used for serial connections. Although this connector is used for variety of purposes, but it is mainly used for 10Base-T and 100Base-TX Ethernet connections.