MT-RJ stands for Mechanical Transfer Registered Jack. MT-RJ is a fiber-optic Cable Connector 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

Features:

Low insertion loss(≤ 0.20dB)and high return loss(≥ 55 dB)
Free-floating ceramic ferrule
UL-rated plastic housing and boot
Boots in a variety of colors
High precision alignment connector

Applications:

Local Area Networks (LANs) and Wide Area Networks (WANs)
Fiber Optic CATV, FTTH, FTTB, FTTP etc
Fiber Optic telecommunication systems
Transmission Mode (ATM)
Fiber Optic Backbone
Military Instrumentation