The word karma itself comes from the Sanskrit language, and is often translated as an act of volition, an effect, destiny or an action. It is important to understand that it is the action itself, not necessarily the good or bad results of that action. Some Eastern religions call these inevitable reactions vipaka. Karma and vipaka are considered to be the basis for a cosmic law of cause and effect, although many Westerners use the word by itself to suggest causality.
The concept of karma is central to both Buddhism and Hinduism, since both religions believe in reincarnation as a means of spiritual renewal. In the purest sense, karma is any action willfully performed by a person who understands the goodness or evilness of that act. It is essentially the stone that causes future ripples in a soul's lifestream. The fruits of that action may be seen right away, or they may takes several reincarnation cycles to manifest themselves.
The idea that the effects of karma may not be experienced in one's current lifetime is one incentive for believers to consider each of their actions carefully. The accumulation of bad karma over several lifetimes can cause a person to experience a lifetime of misery and sacrifice. In some Eastern belief structures, it can affect the actual form a reincarnate soul will take. Those with an abundance of good karma may return as higher forms of life, while those who have accumulated bad may become creatures of a lower form.
In the Western sense, many people tend to view it as a cosmic version of "what goes around, comes around" or "you reap what you sow." In one sense, karma does indeed address the idea of causality, or the principle of action and reaction. If someone chooses to commit a criminal act, for example, he or she should be aware that there will be a cosmic price to pay for their action. Consequently, if someone chooses to perform an act of charity, the concept of universal karma dictates his or her selfless action will eventually be rewarded.
Karma is not necessarily experienced in an overt way. One cannot simply perform a good act with the express hope of receiving karmic payback instantaneously. As with the Western belief in God's benevolence towards mankind, karma also works in mysterious ways. A lifetime of performing good works often results in a sense of satisfaction during one's old age, which is essentially the message inherent in this belief.