spat
.700 Nitro Express
Those things all derive from common law, but you can only rely on them in court because they are codified in actual law, or precedent.Common law are principles that can be used in any court when you assert your rights. Common law entails things like due process of law and the right to trial by jury. common law dictates that for a crime to be committed there needs to be an injured party.
The ability to reference common law in court is very limited, and it's basically only where black letter law is unclear.