http://en.wikipedia.org/wiki/KarmaWestern interpretation
An academic and religious definition was mentioned above. Millions of people believe in it and is a part of many cultures and the psyches of millions of people. Others without religious backgrounds, especially in western cultures or with Christian upbringings, become convinced of the existence of Karma. For some, karma is a more reasonable concept than eternal damnation for the wicked. Spirituality or a belief that virtue is rewarded and sin creates suffering eventually leads to a belief in Karma.
According to Karma, performance of positive action results with the reaction of a good conditioning in one's experience, whereas a negative action results in a reaction of a bad response. This may be an immediate result following the act, or a delayed result occurring either in the present life or the next. Thus, meritorious acts may create rebirth into a higher station, such as a superior human being or a godlike being, while evil acts result in rebirth as a human living in less desirable circumstances, or as a lower animal. Some observers have compared the action of karma to Western notions of sin and judgment by God or gods, while others understand karma as an inherent principle of the universe without the intervention of any supernatural Being. In Hinduism, God does play a role and is seen as a dispenser of karma; see Karma in Hinduism for more details. The latter understanding is accurate with regard to Buddhism and Jainism.
Most teachings say that for common mortals, having an involvement with Karma is an unavoidable part of day-to-day living. However, in light of the Hindu philosophical school of Vedanta, as well as Gautama Buddha's teachings, one is advised to either avoid, control or become mindful of the effects of desires and aversions as a way to moderate or change one's karma (or, more accurately, one's karmic results).
Some people have problems with the teaching on karma, often of what exactly the Buddha is asking them to believe in when asking them to have conviction in karma.
* First, action really is happening -- it's not an illusion.
* Second, you really are responsible for your actions. There's no outside force like the stars or some good or evil being acting through you. When you're conscious, you're the one who decides what to do.
* Third, your actions have results -- you're not just writing on the water -- and those results can be good or bad depending on the quality of the intention behind the act.