It’s used in the movement scripts, but I can’t find any documentation on it.
EDIT: Nevermind, found it. http://wiki.roblox.com/index.php?title=API:Enum/PlayerActions
Apparently I missed it when I was first searching for it?
Still kinda sparse documentation though.
From what I’ve seen I believe it’s to link any and all possible controls used to move the player to a single enum, from where it’s easier to connect all devices’ movement input to a custom action. Nonetheless, even the smallest bit of clarification on the wiki is missing so that would be a good thing to add.