RTP ( Return to Player) - is the return to player percentage.
When you open a game you like and its rules, you will find a place that shows the return percentage. For example, the payout percentage for the "NetEnt" game "Starburst" is 96.1, which means that 96.1% of the total amount wagered on the game is paid back to players. However, this percentage does not mean that every player individually will receive this amount of money back.
The payback percentage applies to the game in general, across the entire network, i.e. to all the people playing the game at different online casinos at the same time.