[1] Justification is an exception to the prohibition of committing certain offenses.
Justification can be a defense in a prosecution for a criminal offense.
For example, to intentionally commit a homicide would be considered murder.
However, it is not considered a crime if committed in self-defense.
In contrast, an excuse is a defense that recognizes a crime was committed, but that for the defendant, although committing a socially undesirable crime, conviction and punishment would be morally inappropriate because of an extenuating personal inadequacy, such as mental defect, lack of mental capacity, sufficient age, intense fear of death, lacking the ability to control their own conduct, etc.