n (legal) typically in the phrase "common law system" -- a legal system that gives great precedential weight to common law (in sense 1), as opposed to a civil law, Islamic law, and Soviet law systems.
n (legal) typically in the phrase "common law jurisdiction" -- a jurisdiction that uses a common law system (in sense 2), United Kingdom and most of its former colonies and possessions, including the United States.
n (legal) (archaic) one of two legal systems in England and in the United States before 1938 (the other being "equity").