What Does Registered Jack-11 Mean?
A registered jack-11 (RJ-11) is a 6-position 2-conductor telephone connector/jack (6P2C) with 4 positions unused. In the United States, RJ-11 is commonly used to connect the telephone handset to the base unit, and the entire telephone to the wall outlet.
A registered Jack-11 can also be used to connect LANs, but RJ-45 connectors are more commonly used for this purpose.
Techopedia Explains Registered Jack-11
Registered jack is a standardized construction and wiring pattern providing the physical interface for telecommunications or data equipment. Other standard designs include RJ-14, RJ-21, RJ-45 and RJ-48.
The "RJ" abbreviation actually only refers to the wiring of these types of jacks. However, the plug itself without wires is also referred to by these names, although this is technically incorrect.