All-in
A bet of your entire remaining stack. There is nothing left to bet: either the opponent calls and the hand runs to the end, or the pot is yours immediately.
All-in is a bet of everything you have left. After it there are no more decisions in the hand: if the opponent folds, the pot is yours; if he pays, the remaining cards are simply dealt out and the best hand wins. You cannot lose more than your stack, and you cannot add to it mid-hand.
An all-in looks like a gamble but is counted exactly: once the money is in and the cards are known, each hand's share is computed by enumerating every remaining run-out. The rest is the deck. That is why an all-in that reaches showdown is the one place in poker where the gap between decision and result can be measured in dollars.
An example from session 3
A♠A♦ against K♥K♦, both stacks in before the flop, $121.46 from each side. Aces win 81.71% of run-outs. By equity the hand was worth $75, the actual result was +$118: the 43-dollar difference is a gift from the deck. In another session the same aces against the same kings lose, and the decision to put it all in is exactly as right.
The same in business
An all-in is a decision after which there will be no more decisions: selling the company, leaving a job for your own venture, the whole budget into one channel. It has to be counted before, because afterwards there is nothing to count. And the stake must matter without being critical: whoever bets a stack he cannot afford to lose is counting fear, not odds.
The whole hand is in session 3: “Results and decision quality are kept in different books”.
The other terms are in the glossary.