RTP, or Return to Player, is a percentage that represents the average amount of money a gambler can expect to win back from a particular online casino game over a certain amount of time. In other words, it measures the amount of money that a player can expect to win back in the long run, based on their total wagers. A higher RTP means that a player has a better chance of winning, while a lower RTP means that they have a higher chance of losing.