To chop is to cut something by hacking at it. In many places, there are farms where you can chop down your own Christmas tree.
When you chop wood, you usually hit it with an axe, splitting each length into narrow pieces. A chef uses a knife to chop, hacking an onion into tiny bits, for example. When it's a piece of meat that's cut so it's attached to a bone, such as part of a rib, it can be described as a chop — like a lamb chop. And if someone claps his hands at you and says, "Chop-chop!" he means "Hurry up!"