1. An interjection used as a warning for imminent danger or something that one needs to be aware of. "Heads up!" he shouted as the brick fell off the edge of the building. Heads up, the boss is looking for you and she looks angry!

2. noun A preliminary notice, especially of future difficulty, trouble, or danger; a warning. Often hyphenated. Make sure everyone gets the heads-up about the inspection tomorrow morning. We don't want anyone coming in unprepared. Hey, just a heads-up—the boss is in a foul mood, so don't do anything to attract attention to yourself! Just give me a heads-up if you need a ride.