House advantage, sometimes called 'house edge', is one of the most important gambling concepts to understand because it implies that when you gamble, you should expect to lose money. The house always has the advantage.
"House advantage" refers to the mathematical formula used to ensure the gaming operator (e.g. the casino) always makes money. While it's possible to win in the short-term, games are designed to keep more money than they pay out in winnings over the long term. The house advantage can range from fairly small (less than 1% for blackjack players using basic strategy) to quite large (around 10% for slots, up to 25% for some table game side bets). These numbers represent the average amount of all wagers that players will lose over the long term. This means there is a cost to gamble. You may win occasionally but expect to spend money over time.
Return To Player
Return to player (RTP) can be seen as the opposite of house advantage. For example, if a slot machine is programmed with a house advantage of 8 percent, the average RTP will be 92%, meaning that over time the machine will keep about 8% of all money bet and will return 92% in the form of winnings and prizes to players over the life-time of the machine. Like the house advantage, the return to player is typically calculated on initial bets only and not on additional bets or side wagers.