First stage regulator ports:
7/16" port = HP
3/8" port = LP (or IP)
1/2" port = MP

First stage regulator pressure:
high-pressure = HP
low-pressure = LP, IP, or MP

"Low" is sometimes called "Intermediate" or "Middle" pressure and all three terms are referring to the exact same regulated output pressure of the first stage.

Scuba hose connectors
second stage 9/16" = LP
inflation Shrader = BC

Mated fittings that can be quickly disconnected without tools = QD