Definition from Wiktionary, the free dictionary
Alternative forms 
- Very tired.
- (chiefly UK) With everything included.
- (poker) Being without any further money to bet, but remaining active in a hand
- By betting his last $100, John was all in.
- (poker) A hand where at least one player bets all of his or her chips.
- (poker) A player who is all in.
- Since she was against an all in, Jill had no reason to bet.