These are the terms that come up when people talk about how slot machines work and when a few of them are worth playing. Each definition is short on purpose; the linked pages go deeper.
- RNG (random number generator)
- The software that picks every spin's outcome at the instant you press the button. It has no memory of earlier spins, so streaks, timing and bet size do not change what comes next.
- RTP (return to player)
- The long-run share of money wagered that a game pays back, for example 90%. It is an average over a very large number of spins, not a promise about one session.
- Volatility (variance)
- How the return arrives. A low-volatility game pays small amounts often; a high-volatility game pays rarely and in larger pieces. It sets how wide the swings are, not the average cost.
- Hit frequency
- How often a spin pays anything at all. A game can hit often and still return little, because most of those hits are smaller than the bet.
- Paytable
- The table of symbols, combinations and prizes. It is where the casino's edge is set, which is why timing a machine does not beat it.
- Denomination and bet level
- The value of one credit and the number of credits wagered per spin. Together they set what a spin costs and, on some games, which meters advance.
- Progressive jackpot
- A prize that grows as players wager, shown on a meter above the machine. Standard progressives can climb without a limit.
- Must-hit-by progressive
- A progressive guaranteed to pay before its meter reaches a stated ceiling. The nearer the meter is to the ceiling, the less the next player pays to reach it. See must-hit-by progressives explained.
- Reset (seed) value
- Where a progressive meter starts again after a payout. The gap between the reset value and the ceiling is what the current meter reading is compared against.
- State
- Anything visible on a machine that carries over to the next player: a meter, a coin count, a counter, a built-up board. Most machines carry none. See slot machines that carry state.
- Advantage play
- Playing only when a machine's visible state makes a spin worth more than it costs, and leaving when it does not. It is a long-run edge, not a guaranteed result. See can you beat slot machines?
- Hold & Spin
- A bonus in which special symbols lock in place while the remaining positions respin. On some games a hidden or visible counter forces it to trigger by a set point.
- Bankroll
- The money you set aside for play and can afford to lose. It is a budget for entertainment, not an income.
- Loss limit
- The amount you decide before you sit down at which you stop. It is the main protection against high-volatility swings. See slot bankroll and variance.
Where to look next
- How slot machines work: RNG, RTP and volatility in context.
- Can you beat slot machines? What works, what doesn't, and why.
- All 360+ machine guides.
If gambling stops being fun, call 1-800-GAMBLER.
Frequently asked questions
What does RTP mean on a slot machine?
RTP (return to player) is the long-run share of money wagered that a game pays back, for example 90%. It is an average over a very large number of spins and says nothing certain about a single session.
What is the difference between RTP and volatility?
RTP is the average cost of playing. Volatility is how that average arrives: low-volatility games pay small amounts often, high-volatility games pay rarely and in larger pieces.
What is a must-hit-by progressive?
A progressive jackpot that is guaranteed to pay before its meter reaches a stated ceiling, so a meter close to the ceiling costs the next player less to reach the prize than one that just reset.