Since I was A2A the original question (now changed) I feel obliged to update my answer to include “law” in addition to “legal theory.”
In the broadest sense, “jurisprudence” is the study of the nature of law, methods of legal reasoning, legal systems, and legal institutions. Its study covers such concepts as how we know what law is, what are the sources of law and any obligation to obey it, and what difference there is between law and justice. Often included is analysis of how competing concepts of liberty, equality, neutrality, and choice of law affect judicial decisions. The focus is on the practical application of legal concepts.
“Legal theory” is more strictly academic, since it is the examination of different intellectual traditions that have shaped the law: natural law and natural rights, legal positivism, legal realism, Marxism, feminist legal theory, and postmodern legal theory.
“Law”is a system of rules regulating the activities of a particular group of humans and penalties for breaking those rules.