RTP stands for Return to Player and indicates what share of all wagers placed on a game is, on average, paid back to players over a very long period — statistically, over millions of rounds. An RTP of 96% means that, of every 100 units wagered, on average 96 units come back over the long run.
It's a theoretical long-term average, not a guarantee for any single session. In a short session of minutes or hours, the actual result can swing well above or below the RTP, for better or worse. That's down to the game's volatility (or variance), not RTP itself.
A game with a high RTP but high volatility can still produce losses over long stretches before paying out rare, larger wins. A game with lower volatility tends to pay smaller amounts, but more often. Looking at both figures together gives a more realistic picture than RTP alone.
Reputable software providers usually publish the RTP directly within the game (often under the rules/info section) or in their official game sheets. Important: the same slot can exist with different RTP configurations, so the actual value in play can vary slightly from platform to platform.
RTP is useful for comparing games against each other within a given operator, not for predicting the outcome of your next session. As a rough guide, values from around 96% upward are generally considered relatively player-friendly — in no case is it a guarantee of winning.