RTP and volatility are the 2 most important mathematical characteristics of a slot game. They basically influence how much and how often you win.
RTP (return to player, payout ratio or payout percentage) is the long-term statistical rate of total money won divided by total money wagered. This means that if the RTP of a game is 96%, and you start with €1,000,000,000 and then play 1,000,000,000 rounds at €1 each, then you should end up with approximately €960,000,000.
If you only play a few hundred rounds, your current return could vary between 30% and 1000%. But the more rounds you play, the more likely you are to be closer to the statistical RTP of the slot game. This is why such large numbers were used in the example above.
The most common RTP for bitcoin slot machines is around 96%. Some slots like Blood Suckers feature an RTP up to 98%.
RTP is a very popular feature of online slots as it can be expressed as a single number. It is easy to compare, and most game providers state the RTP of each slot game.
RTP can be used for various simplified calculations, such as how much you can expect to lose on a bonus when playing.