MT-RJ stands for Mechanical Transfer Registered Jack. MT-RJ is a fiber-optic CableConnector that is very popular for small form factor devices due to its small size. Housing two fibers and mating together with locating pins on the plug, the MT-RJ comes from the MT connector, which can contain up to 12 fibers.
The MT-RJ is commonly used for networking applications. Its size is slightly smaller than a standard phone jack and just as easy to connect and disconnect. It’s half the size of the SC Connector it was designed to replace.