From Buddhism: Karmic Action

Ahosi Kamma ‘action that was’ with the implication that it is no more. The doctrine of karma involves the active and the passive aspects of the process of mental volition. All the various classifications of types of karma have the efficacy of action in view, as functional, as productive, as intensive in its own sphere, or as extensive in duration and time. When action ceases to be re-active, this may be due to its force having been obstructed or even destroyed by other influences. It may be that, owing to a lack of opportunity to react immediately, the karmic force is lying in abeyance accumulatively. But, when action with volition is not given any opportunity, either here or hereafter, not through having spent its reproductive energy, or through destructive opposition, but merely through lack of time or appropriate conditions, it is said: “There has been action, there has been no karma-result, there will be no karma-result, and there is no karma-result now.”

As most types of action, however, have an inherent accumulative power of reproductivity without being bound by a time-limit, it is mostly that kind of action which must become reactive in this life itself which will become inoperative and ineffective as ahosi kamma, once the limit of this life span has been passed. Its potential force having lapsed, it cannot be revised again: just as a man who has been acquitted in a murder-trial cannot be tried for that same case. Another reason for karmic action becoming inoperative is the intrinsic weakness of an action. Thus, a thought arising as the seventh thought-moment of apperception is not strong enough to carry its effect beyond a second birth; and if such thought does not become subsequently effective, it also will be an action that was. “All ineffectual volition, by reason of their inherent weakness, and all time-barred kamma-s, by reason of their inhibition by more powerful kamma, are termed ‘have-not been-s’.”