Casino advantage is the mathematical edge that every casino game builds in for the house. It is usually called the house edge, or simply the edge, and is expressed as the average percentage of each stake the casino expects to keep over a very large number of rounds. Without it, casinos could not stay in business.
The figure is the mirror image of RTP: a slot with an RTP of 96% carries a 4% house edge. The advantage changes from game to game, between variants of the same game, and with small rule changes — whether a blackjack dealer stands on soft 17, for instance, or whether a roulette wheel has one zero or two.
In any single session, players can and do win; the edge only shows over time. For operators, it underpins revenue forecasts and bonus design, and many regulated markets require game RTPs to be tested and published.