There is no duty to retreat inside one's home, or place of business. For deadly force to be justified it must be in defense of one's self or others. The person must believe that there is a real threat of death, or bodily injury, and all other means of defusing the situation must have be exhausted before using deadly force. Deadly force may not be used in the sole defense of 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.