To ad-lib means to make something up on the spot without planning or preparation ahead of time.

When an actor forgets their lines during a play, they might ad-lib by inventing dialogue that fits the scene until they remember what they're supposed to say. A speaker who loses their notes might ad-lib the rest of their presentation, relying on their knowledge and quick thinking. Musicians sometimes ad-lib by improvising melodies or solos that weren't written in the original music.

Ad-libbing requires confidence and creativity. You need to think fast and trust your instincts. A good ad-lib often feels natural, as if it had been planned all along. The best comedians are skilled at ad-libbing jokes during their performances, responding cleverly to unexpected situations or comments from the audience.

The word can work as a verb (“She had to ad-lib her way through the speech”) or as a noun (“That funny line was an ad-lib, not part of the script”). When you successfully ad-lib, you're using your knowledge and creativity to handle an unexpected situation smoothly.