Karma is best described as the law of cause and effect. It’s the consequences of your actions. It’s the energy, or the ambiance of a situation.
People talk about good karma and bad karma, but there’s really only just karma; whether it is good or bad depends on what you’ve done to incur it, and what you do to bring it back into balance. The actual word karma is from the Sanskrit language, and it is used in Buddhist and Hindu principles. Some believe that karma carries on from lifetime to lifetime, and that through reincarnation you can in this existence work on bringing into balance your karma from previous incarnations.