House edge is the percentage of the built-in advantage that casinos have on most of the games played on the gaming floor. In slots, the house edge is around 5 to 12%. For tables games, commonly around 6% to 2%, but of course there are some exceptions. For example, poker or mahjong, in which the casino will take a rake (like a service charge from the total pot), or charge per usage time. Also, in blackjack depending on the remaining cards in the deck, there are situations where the player will theoretically have the edge, although deciphering such a situation is very difficult.
As George Clooney said in Oceans 11, “the house always wins”, but not always.