term:

Justification

justification n

1 : the act or an instance of justifying
2 : something that justifies
;specif
: a legally sufficient reason or cause (as self-defense) for an act that would otherwise be criminal or tortious
3 : the affirmative defense of having a legally sufficient justification compare excuse

Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.