Justification and Excuse
The common law as well as the Model Penal Code classifies defenses as either justifications or excuses.
The difference between justification and excuse is explained in the commentaries to the Model Penal Code "[t]o say that someone's conduct is 'justified' ordinarily connotes that the conduct is thought to be right, or at least not undesirable." . . ."to say that someone's conduct is 'excused' ordinarily connotes that the conduct is thought to be undesirable but that for some reason teh actor is not to be blamed for it.
In some case, a given defense may act as both a justification or excuse.
- Model Penal Code Commentaries Article 3, introduction, at 3