House advantage, sometimes called house edge, is the concept that the gaming operator always has the advantage, and over time you should expect to lose money.
"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 gambling. You may win occasionally but expect to spend money over time.
Return To Player
Return to Player (RTP) is a term used to describe the percentage of winnings paid to players over a period of time. It is also a different way of stating the House Advantage. Using the slots example from above (10% house advantage), the RTP for this slot would be 90%.
But remember that outcomes are random and Return to Player is calculated over the whole life cycle of the game, not an individual player’s experience.