Definition from Nolo’s Plain-English Law Dictionary
The method of studying law used in most American law schools, in which students read and outline (brief) appellate opinions (cases), then hear lectures about them and discuss them. Each case stands for a particular rule of law and is printed in "casebooks" on particular topics (such as contracts, torts, criminal law, and constitutional law). The case system is reinforced by textbooks and outlines on the subject matter, which were formerly the principal sources of learning. The method was introduced at Harvard in 1869 by professor Christopher C. Langdell and soon became standard.