I'm no hockey expert and i may be totally wrong, but i believe hooking is a penalty they call when you use your stick to trip someone, or something like that. So they penalize your team by sitting out a player for two minutes.
Slang term hooking = prostitution.
edit - i was slightly off, it's
the act of impeding or obstructing an opponent's progress by placing the shaft or blade of the stick on the midsection of the opposing player and pulling him or her back. Hooking is illegal and normally results in a minor penalty being assessed to the offending player.