To fret means to worry anxiously about something, often repeatedly turning the problem over in your mind without making progress toward solving it. When you fret about an upcoming presentation, you keep imagining everything that might go wrong instead of simply preparing. When your mom frets about whether you remembered your lunch, she's worrying even though there's nothing she can do about it now.

If you're concerned about a math test, you might review your notes or ask for help. But if you're fretting about it, you're probably lying awake imagining failure, replaying your worries in circles. People who fret a lot are sometimes called fretful, like a fretful baby who can't settle down or a fretful dog pacing by the door.

A completely different meaning of fret is one of the raised metal strips on the neck of some stringed instruments like guitars, which help players place their fingers to change the notes they play.