\Kar"ma\, n. [Skr.] (Buddhism) One's acts considered as fixing one's lot in the future existence. (Theos.) The doctrine of fate as the inflexible result of cause and effect; the theory of inevitable consequence.
however, it's not a mystical force that comes and gets you it's just common sense.
for example, you walk down the street and smile at someone they smile back. you punch someone, they punch you back.
it works on a higher level too though, like if your whole community gets together and does something good, then another community will try to do the same.