Provably Fair is a technology which allows the gambler to verify the fairness of every play. In a Provably Fair gambling system the player has the chance to check every play using Server Seed, Client Seed and Hash. You can enter these details to the Provably Fair tool of the Bitcoin Casino site and verify the randomness thus fairness of the payout outcome you got. In a simplified way, players can always check that the outcome of every game round is fair and wasn't tampered with. As such, cheating is arguably impossible.