A more thorough explanation:

The retreat rule is a doctrine in criminal law that states that if someone is being attacked, they must try to retreat to a safe place before using deadly force in self-defense. This is unless the person being attacked is in their home or place of business, or if they are trying to arrest the attacker. The idea behind this rule is that human life is important and should be preserved whenever possible.

For example, if someone is walking down the street and someone else starts attacking them, the person being attacked should try to run away or find a safe place to hide before using a weapon to defend themselves. However, if someone breaks into their home and starts attacking them, they are allowed to use deadly force to protect themselves without trying to retreat first.

It's important to note that not all jurisdictions follow the retreat rule. Some places have a "no-retreat" rule, which means that people are allowed to use deadly force to defend themselves without trying to retreat first.