What is Kamma?
Kamma or karma is an impersonal, natural law that operates in accordance with our actions. It is a law in itself and does not have any lawgiver. Kamma operates in its own field without the intervention of an external, independent, ruling agent. In the language of the harvest, kamma can be explained in this way: if you sow good seeds, you will reap a good harvest. If you sow bad seeds, you will reap a bad harvest. In the language of science, kamma is called the law of cause and effect: every cause has an effect. Another name for this is the law of moral causation. Moral causation works in the moral realm just as the physical law of action and reaction works in the physical realm.
Kamma is simply action. Within animate organisms there is a power or force which is given different names such as instinctive tendencies, consciousness, etc. This innate propensity forces every conscious being to move. He moves mentally or physically. His motion is action. The repetition of actions is habit and habit becomes his character. In Buddhism, this process is called kamma.
In its ultimate sense, kamma means both good and bad, mental action or volition. 'Kamma is volition,' says the Buddha. Thus kamma is not an entity but a process, action, energy and force. Some interpret this force as 'action-influence'. It is our own doings reacting on ourself. The pain and happiness man experiences are the results of his own deeds, words, and thoughts reacting on themselves. Our deeds, words and thoughts produce our prosperity and failure, our happiness and misery.
Buddhists believe that man will reap what he has sown; we are the result of what we were, and we will be the result of what we are. In other words, man is not one who will absolutely remain to be what he was, and he will not continue to remain as what he is. This simply means that kamma is not complete determinism. The Buddha pointed out that if everything is determined, then there would be no free will and no moral or spiritual life. We would merely be the slaves of our past. On the other hand, if everything is undetermined, then there can be no cultivation of moral and spiritual growth. Therefore, the Buddha accepted neither strict determinism nor strict undeterminism.
Source: What Buddhists Believe by Dr. K. Sri. Dhammananda