What is this?
-------------
an inventory item to climb walls etc.

----------------------------------------
Ingame console commands (or keybinding):
----------------------------------------
hook
is used in 3 ways:
a) if you have no hook in use --> fires the hook in the current aiming direction
b) if you just fired the hook --> stops the action
c) if the hook is set --> release it

After setting the hook the rope will slowly release you to the ground, so use

hookup
--> to climb back to the top position of the rope