Hey everyone, I wanted a little clarification on what exactly boarding is?

I know that you cannot hit someone into the boards when they are like three or four feet out because they might hit their heads or whatever, but are there other calls for boarding too?

If you remember when the Pens played in Anaheim with like five seconds left in the entire game, one of the Ducks got called for boarding Orpik, but he was up against the boards, only his head was down, as in bent over.

If someone could clear this up that would be cool, all of the sites I've looked up said it's just the three to four foot rule and nothing else.