The entire collection of published legal decisions of the courts which, because of stare decisis, contributes a large part of the legal rules which apply in modern society.
If a rule of law cannot be found in written laws, lawyers will often say that it is a rule to be found in "case law". In other words, the rule is not in the statute books but can be found as a principle of law established by a judge in some recorded case.
The word jurisprudence has become synonymous for case law.