Establish a usage, tradition, or standard to be followed in the future. For example, He set a precedent by having the chaplain lead the academic procession. The word precedent here signifies a previous instance or legal decision upon which future instances are based, a usage dating from the early 1400s.

What does it mean to set precedent?

: to decide something that will be used as an example or rule to be followed in the future The ruling in the case is likely to set a precedent for how future cases are decided.

Is it set a precedent or set a precedence?

"Precedence" means priority or preference. It pertains to ranking. "A precedent" is a previous example used to guide a decision (often in law). "Precedents" is the plural.