Registered Jack

I regularly throw out terms without really knowing what they mean, like the "RJ" used as a prefix for telephone (RJ-11) or Ethernet (RJ-45) cabling.  I now know that "RJ" stands for "Registered Jack", but the real eye-opener was that the aforementioned RJ-45 used for computer networking is really
an 8P8C.  But I guess that mouthful is a bit much, so RJ-45 stuck.

https://en.wikipedia.org/wiki/Registered_jack

https://en.wikipedia.org/wiki/Modular_connector