All-out means using every bit of your effort, energy, or resources without holding anything back. When you make an all-out effort to finish a difficult project, you give it everything you've got, pushing yourself to your absolute limit.

The phrase suggests total commitment. An all-out sprint in gym class means running as fast as your legs can possibly carry you until you cross the finish line. An all-out war means nations are fighting with all their military power, not just small skirmishes. When your soccer team launches an all-out attack in the final minutes of a close game, every player pushes forward, trying to score.

You can also use all-out as an adverb: “The students went all-out to raise money for the food bank.” The word captures that moment when you decide not to hold back, when you commit completely to achieving something, when you throw everything you have into the effort. It's the opposite of halfhearted or cautious.