RTP is a game’s long-run average return: 96% RTP means a 4% house edge....

https://varimail.com/articles/does-session-timing-matter-in-online-casinos/

RTP is a game’s long-run average return: 96% RTP means a 4% house edge. Volatility describes how uneven wins and losses may be. In a short session, results can differ sharply from the average—there’s no guaranteed return.