Your "rightful" share of a pot. If the pot contains $80 and you have a 50% chance of winning it, you have $40 worth of equity in the pot. This term is somewhat fanciful since you will usually either win $80 or $0 (unless the pot is split), but it gives you an idea of how much you would expect to win on average over multiple instances of the same situation. Also sometimes used more broadly as a synonym for "value."