The Castle Law, often referred to as "Castle Doctrine," is a legal principle that allows individuals to use reasonable force, including deadly force, to defend themselves against an intruder in their home or, in some jurisdictions, other places where they have a legal right to be. The name derives from the idea that one's home is a "castle" that should be defended without the obligation to retreat. 

Key aspects of the Castle Doctrine include:

1. **No Duty to Retreat**: In situations where an individual is threatened in their home, they are not required to retreat before using force.
2. **Reasonable Force**: The force used in self-defense must be proportional to the threat faced. Deadly force can typically be used if the individual believes they are in imminent danger of death or serious bodily harm.
3. **Protection of Property**: In some jurisdictions, the doctrine extends to defending property, allowing for force against intruders who unlawfully enter one's dwelling.

The specifics of Castle Law can vary by state or country, so it is important to understand local laws for detailed applications.