Depends whether you want the Western or Eastern definition, Ina.
As you can probably guess, the Western version has been streamlined, optimized and given it's own Speed-E Check Out line. In essence, Westerners believe that karma is "what goes around comes around", just like Davey said.
But as with most things Eastern, what we see on the surface is only a very small piece of the whole.
See, we look at it as some kind of Heavenly Revenge system - if someone wrongs us, his/her karma is gonna' catch up to them. It's Superman and Johnny Cochran and Chuck Norris all rolled into one gigantic being, so if they can't sue you they'll kick your butt into next week.
Easterners see that as only a very small part of karma, if indeed it is seen that way at all. For all its supposed importance, karma is only one of 24 main precepts of Buddhist thought. Not
everything is due to karma. The Buddha himself contradicted the misinterpretations:
[FONT=Arial, Helvetica, sans-serif]"So, then, according to this view, owing to previous action men will become murderers, thieves, unchaste, liars, slanderers, covetous, malicious and perverts. Thus, for those who fall back on the former deeds as the essential reason, there is neither the desire to do, nor effort to do, nor necessity to do this deed, or abstain from this deed." [/FONT]
Basically what he was saying was that if our entire present life was totally due to what we did in
previous lives, then the concept of free will was a lie, and Buddha was many things but he wasn't a dummy. Momma Buddha didn't
raise no dummies.
In fact, Buddha's words on this matter pointed out that there was really very little difference between the erroneous view of karma and a belief in God. Now, remember that Buddha (and Buddhists) do not believe in God. What he was trying to tell his followers was that thinking that your life was preordained by karma was just as ridiculous a notion as an all-powerful Being who controls our fate and destiny.
To go even further I'd have to explain how, in addition to the 24 precepts I mentioned earlier, karma is also one of 5 main
niyama ("processes") that seek to explain natural laws and causes-and-effects, but this is already turning into an Eastern Religions 101 term paper so I'll stop.
