Ref is short for referee, the person who enforces the rules during a sports game or match. The ref watches the action closely, blows a whistle when players break rules, and makes decisions about penalties, points, and whether plays count. In basketball, the ref calls fouls when players push or grab illegally. In soccer, the ref can give yellow or red cards to players who commit serious violations.

Being a ref requires quick thinking and courage: you have to make split-second decisions while players, coaches, and fans are all watching and reacting. Sometimes everyone disagrees with a call, but the ref's job is to be fair and consistent, not to make everyone happy. Good refs stay calm under pressure and stick to their decisions even when the crowd boos.

People also use ref as a verb, meaning to serve as a referee: “Will you ref our pickup basketball game?” Outside of sports, someone might jokingly say “I'm not ref this argument” when two friends are bickering and want them to pick a side.