What is karma?
Cause and effect. Whatsoever a man soweth, that he shall also reap. For each action there is an equal and opposite reaction. There are a lot ways to describe karma, but it is essentially the belief that your present circumstances are the product of previous actions, and what you do today will affect what happens tomorrow. Karma is also associated with past lives -- each time you're reborn, the energies from your previous lives influence the conditions of your current life.