1. Fully committed to a task or endeavor; giving or prepared to give all of one's energy or resources toward something. Just so you know, I'm all in if you're serious about taking that cross-country trip next week.

2. Betting all of one's money in a card game, such as poker. Once I got my best hand of the night, I went all in.

3. Completely exhausted, fatigued, or worn out. I was all in after only the first mile of the race; I could barely even walk for the rest of it!