Common Law

What Does Common Law Mean?
In the United States, a body of unwritten laws based on precedents established by the courts. Common law is used in deciding novel cases where the outcome cannot be determined based on existing statutes. The U.S. common-law system evolved from the precolonial system of English common law.

Investopedia explains Common Law
The decisions (precedents) of higher courts are binding on lower courts so that the U.S. legal system will have consistency and stability. However, lower courts can choose to modify precedent or distinguish from precedent if precedents are outdated or if the current case is substantially different from the precedent case. Lower courts can also choose to overturn precedent, but this is rare.