What is Duty To Retreat?

Legal Definition
In criminal law, the duty to retreat, or requirement of safe retreat, is a legal requirement in some jurisdictions that a threatened person cannot stand one's ground and apply lethal force in self-defense, but must instead retreat to a place of safety.

is a specific component which sometimes appears in the defense of self-defense, and which must be addressed if the defendant is to prove that his or her conduct was justified. In those jurisdictions where the requirement exists, the burden of proof is on the defense to show that the defendant was acting reasonably. Elements of acting reasonably include that the defendant had first avoided conflict and, secondly, had taken reasonable steps to retreat and so demonstrated an intention not to fight before eventually using force.
-- Wikipedia