The extra money you can win after hitting, counted in the call decision.
Even if the current pot doesn't give you the required equity, you can call if adding what you win after hitting gets you there. Remember them as "misses to hits": flush 4 to 1, open-ender 5 to 1, gutshot 11 to 1. Example. On a flush draw facing 5 into 10, you need to collect 5 × 38 ÷ 9 = about 21. There is 15 now, so call if you can win about 6 more after hitting. They grow with a deep opponent who doesn't fold, a draw that is hard to see, and a draw to the nuts.