CTCSS / PL / CG
In Repeater Early days, “PL” was used to keep stations out - ie, “Closed” Repeater. Available to members only.
Now, because there are so many repeaters, and frequency pairs are becoming scarce, “PL” allows a user to “Select” which Repeater one brings up in overlapping areas.
Also Used to keep Interference out of Repeater.