There are two kinds of walls: Bearing walls and non-bearing walls. Knowing which can be critical. You can do anything you like to a non-bearing wall, but if you remove or even cut open a bearing wall, you can literally bring down the house. Check the joists or rafters in your basement or attic; if they run perpendicular to the wall in question, it is almost certainly a bearing wall. If they run parallel, it is not.