The house edge is the casino’s built-in mathematical advantage on a game, shown as the percentage of each stake it expects to keep over the long run. It is the mirror image of return to player (RTP). A slot with 96% RTP has a 4% house edge, so on average 4 of every 100 wagered stays with the operator.
The number is theoretical. It describes results over hundreds of thousands of rounds, not a single session, and a player can still win two hands in a row against any edge. It is not a fee either: unlike a commission, nothing is charged on each bet. The edge depends on the game and the rules. Single-zero roulette carries 2.70% and the double-zero wheel 5.26%, while blackjack rules such as 6 to 5 payouts push the figure up.
For operators, house edge is the starting point for revenue forecasts, game mix decisions and bonus wagering contributions.