http://www.buddhanet.net/fundbud9.htm
If karma is not fate or
predestination, then what is it? Let us look at the term itself.
Karma means action, means "to do". Immediately we have an
indication that the real meaning of karma is not fate because karma
is action. It is dynamic. But it is more than simply action because
it is not mechanical action. It is not unconscious or involuntary
action. It is intentional, conscious, deliberate, wilful action.
How is it that this intentional, wilful action conditions or
determines our situation? It is because every action must have a
reaction, an effect. This truth has been expressed in
regard to the physical universe by the great physicist Newton who
formulated the law which states that every action must have an
equal and opposite reaction. In the moral sphere of
conscious actions, we have a counterpart to the physical law of
action and reaction, the law that every intentional, wilful action
must have its effect. This is why we sometimes speak either of
Karma-Vipaka, intentional action and its ripened effect, or we
speak of Karma-Phala, intentional action and its fruit. It is when
we speak of intentional action together with its effect or fruit
that we speak of the Law of Karma.