What is the meaning of “justification” in law?

To “justify” something means to show the justice or rightness of that thing: Concise Oxford Dictionary of Current English (9th ed. 1995), at p. 737. In criminal or tort law, a “justification” describes “actions we consider rightful, not wrongful” because they were taken in circumstances that reveal their rightness, for example, “[t]he police officer who shoots the hostage-taker, the innocent object of an assault who use[d] force to defend himself against his assailant, the Good Samaritan who commandeers a car and breaks the speed laws to rush an accident victim to the hospital ...” (Perka v. The Queen, 1984 CanLII 23 (SCC), [1984] 2 S.C.R. 232, at p. 246).