To flunk means to fail, especially a test, course, or grade in school. When you flunk a math test, your score falls below passing. When a student flunks a class, they don't earn enough points to move forward and might have to repeat it.

The word carries a sense of definite, unmistakable failure rather than barely missing the mark. Someone who scores 68% when 70% is passing didn't quite make it, but someone who scores 45% flunked. Teachers might say a student is flunking out of school when failing grades force them to leave.

You can also flunk someone else: a tough professor might flunk half the class if their work doesn't meet standards. Outside of school, people sometimes use flunk more playfully. You might say you flunked your driving test, or that you flunked your attempt to bake cookies when they turned into charcoal.

Flunking can show that someone needs to study differently, ask for help, or manage their time better, and it can be a chance to learn, improve, and try again.