A refresher is something that helps you remember or relearn information you've studied before. When you take a refresher course in swimming after not swimming all winter, you're reviewing the strokes and techniques you already know but might have gotten rusty on. A math teacher might give the class a refresher on fractions before starting a unit on decimals, quickly reviewing what everyone learned last year.

Knowledge can get a little stale or fuzzy when you haven't used it in a while. A refresher brings it back to the front of your mind, making it sharp and clear again.

You might need a refresher on Spanish vocabulary before a trip to Mexico, or a refresher on the rules of chess before playing your first game in months. Even experts use refreshers: pilots regularly take refresher training to keep their skills current, and doctors attend refresher courses on medical procedures they don't use every day. The key idea is that you're not learning something completely new. You're dusting off knowledge that's already there and bringing it back to life.