To crack the nut is to win enough to cover every cost of playing and still come out ahead. For a land-based player, the nut is more than the losing bets: it includes travel to the casino, a hotel room for the night, meals and drinks. Only money won above that total counts as real profit. The phrase probably borrows from the idea of a tough nut to crack.
Online players have far fewer costs, but the idea still applies to anyone who measures results honestly. Venues use the same expression: a casino or card room cracks its nut when its revenue covers fixed overheads for the period, and only what comes after that is profit.
The operator’s nut
For an online casino, the nut is the monthly cost base: platform fees, game and payment provider charges, licence costs, marketing and staff. Working out the gross gaming revenue needed to break even is one of the first steps when choosing between turnkey, white label and self-service models.