Definition - What does Case Law mean?
Case law is the law that is derived from written judicial opinions as opposed to the law that is created by legislature. While it's the job of legislative bodies to create the law, it's the responsibility of the judicial system to interpret the law. It is these interpretations that become case law.
Case law is frequently referred to as common law.
Justipedia explains Case Law
The philosophy behind having a system that follows case law is that it provides consistency to interpretations and the outcome of cases. A common law system, like that of the United States, gives great deference to the precedent that is set by case law. Therefore, when deciding on a case that is similar to a past case, the system must defer to the decision that was made in the earlier case.