It's understandable if you were laid off given the rocky economy or circumstances beyond your control. You don't have to share the dirty details, but you should be truthful and mention that your company had to let go of X number of people or the department was being restructured.
If you are leaving because of a negative situation, be sure not to badmouth your old company or boss. It just reflects badly on you if you do. You can focus on the fact that you're looking for growth and that you feel this company feels like the step in the right direction.
