For questions about the or a theory or philosophy of law: the concept of law, the nature of law, law and morality, interpretive approaches, etc. Not to be used generally to refer to case-law. Law schools sometimes use "Jurisprudence" in this way.
This is for theories or schools of law such as Originalism, Natural Law, Legal Realism, and the like. It is also for question about the general theory or philosophy of law.