Something done or said that may be an example or rule to guide later acts of a similar kind.
Example:
When Judy bought Christmas presents for all her relatives one year she claimed that it set no precedent, but it did.
The Supreme Court relies on precedents, earlier laws or decisions that provide some example or rule to guide them in the present case. Sometimes, as in the famous 1954 ruling that ordered public schools desegregated, the precedent lies in the Constitution and its Amendments.