Volatility measures how widely results scatter around the average return. A game rated low pays modest amounts at a steady pace, and a game rated high concentrates its return in rare, large wins, often inside a bonus feature. Studios describe it on scales of three or five levels, sometimes with lightning bolts or bars instead of numbers, and the scales are not comparable between studios. Choosing a level is a matter of taste and budget, while the cost over the long run stays put.
Many slots cap the largest win a single spin can produce, often as a multiple of the stake. Once the cap is reached, the round ends and any further winnings are forfeited, which trims the top of the payout range. Games that sell entry to their bonus round list a separate return for the bought feature, sometimes higher and sometimes lower than the base game. Both figures sit in the paytable or the rules, and both change what a large stake can actually return.
Measured returns drift away from the theoretical figure over any stretch a person can play, and the gap narrows only across millions of spins. Tracking sites that pool results from many players show this clearly: a game can run far above or below its figure for weeks. Demo modes normally use the same maths as real play, so a free session shows the rhythm of a game, although a short demo run says as little about the true return as a short session for money.