Retreat rule is a principle of criminal law that a victim of a murderous assault can choose a safe retreat instead of resorting to deadly force in self-defense, unless the victim is at home or in his or her place of business or the assailant is a person whom the victim is trying to arrest. This rationale behind the rule is that human life, even the life of an aggressor, is sufficiently important that it should be preserved when to do so requires only the sacrifice of the much less important interest in standing one's ground. Only very few states in the U.S. have adopted this rule.
This rule is not intended to enhance the risk to the innocent; its proper application has never required a faultless victim to increase his assailant's safety at the expense of his own. On the contrary, he could stand his ground and use deadly force otherwise appropriate if the alternative were perilous, or if to him it reasonably appeared to be. [United States v. Peterson, 483 F.2d 1222, 1235-1236 (D.C. Cir. 1973)]
This is also known as no-retreat rule.