Here is a way to understand the meaning of karma. If you were to perform an action such as shooting an arrow from a bow, that is the cause of the arrow landing somewhere. So karma is the cause of an effect. Just as there are many variables which affect the arrows destination, there are also variables that we may or may not know of that affect the result of our actions. Some karmas have a quick effect, while the effect of others may not manifest during this lifetime. We are born with certain karmic debts and others we create in any given moment. All that we do is karma, fortunately we have choices in the type of karma we create.