Deadly force is only justified when there is a believe of serious injury, death, or to prevent a felony in one's home. Reasonable force may be used when it is believed necessary to defend one's self, others, or property.
Castle Laws are laws that address the use of force when defending one's self inside their home, or on their property. Some states expand this to vehicles, and the person's place of work. Castle Laws generally include: the places where this law applies, the requirements fro use of deadly force, if there is a duty to retreat, the amount of force that maybe used in defending one's self or others. These vary widely from state to state.