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Slot Glossary — A to Z of Slot Machine Terms

ReelWise Editorial · 2026 · Reference document

Every term you'll encounter reading a paytable, review, forum thread, or casino help page — defined in plain language, in one place. Where a term has a dedicated guide, it is linked.

A

All-ways / All-pays

A win structure where matching symbols on adjacent reels from left to right count as a win regardless of their vertical position on the reel. Equivalent to "ways to win." See also: Ways to win.

Ante bet

An optional additional side wager (typically 25–50% of your base bet) that increases the frequency of scatter/bonus triggers. The overall RTP remains the same or similar, but you pay a premium for a higher chance of entering the bonus round more frequently. Governed by paytable rules.

Autoplay

A feature that automatically spins the reels a specified number of times at the selected bet, without requiring the player to press spin each time. Regulated markets often impose controls on autoplay (mandatory stop conditions, win/loss limits).

Avalanche reels

NetEnt's original branding for the cascade/tumbling mechanic, introduced in Gonzo's Quest. Winning symbols disappear and new ones fall from above. See: Cascading reels guide.

B

Base game

The primary game mode, as opposed to a bonus round or free-spins feature. Most of a player's time is spent in the base game; many games concentrate a majority of expected value in the feature rather than the base game.

Bet multiplier / bet multiple

Payouts expressed as a multiple of the total bet (stake) for that spin. A win of 50× on a €1 bet = €50. The most transparent way to express wins as it scales with any bet size.

Bonus buy

A direct purchase mechanic allowing the player to immediately enter the bonus/free-spins round for a fixed multiple of the stake, bypassing the base-game trigger requirement. Prohibited in the UK (UKGC) and restricted in some other markets. See: Bonus buy guide.

Bonus game / bonus round

A separate game mode entered when a trigger condition is met (usually scatter symbols). May include free spins, pick games, wheel spins, or other mechanics different from the base game.

Buy-a-bonus

Alternative term for bonus buy. Same mechanic, different label used by some studios.

C

Cascade (cascading reels)

Mechanic where winning symbols are removed after a win, and new symbols fill their positions from above (or below, in some implementations). If the replacement symbols form a new win, the cascade continues. Also called tumble, avalanche, or rolling reels depending on the studio. See: Cascading reels guide.

Certified RNG

A random-number generator that has been independently tested and certified by an approved testing laboratory to produce statistically random outputs. Required for all games in major regulated markets.

Cluster pay

A win structure where wins are formed by groups of matching symbols touching horizontally or vertically, rather than by pay lines or ways. Cluster sizes vary, and payouts often scale with cluster size. Common in cascade-mechanic games with non-traditional grid shapes.

Coin value / coin size

In games that express bets and payouts in coins rather than currency, the coin value is the monetary denomination of each coin. Total bet = coin value × coins per line × number of lines. This format can obscure the real money value; converting to bet multiples clarifies the picture.

D

Dead spin

Informal term for a spin that produces no win. Also called a non-winning spin or zero-win spin.

Declining reels

A variant of the cascade mechanic where, instead of new symbols falling from above, the existing symbols above the removed ones move down, and new symbols appear at the top. Functionally the same result as a standard cascade.

Dynamic reels

Reels whose height (number of visible symbols per reel) changes each spin, as in Megaways. Each reel independently displays a random number of symbols within a defined range, changing the way count each spin.

E

Expanding wild

A wild symbol that expands to cover the entire reel (or row, in some games) when it lands. Used to increase win coverage. May trigger a respin after expanding in some game designs.

Expected value (EV)

The average outcome of a repeated random event, calculated as the sum of (probability × payout) across all possible outcomes. A slot's RTP is essentially its expected value per unit wagered. EV is negative for the player on a house-edge game by definition.

F

Feature buy

Alternative term for bonus buy. Also sometimes called "direct buy" or "feature purchase."

Fixed paylines

A game structure where the number of active paylines cannot be reduced — all lines are always in play. The stake covers all lines. More common in modern online slots than variable-line configurations.

Free spins

A bonus mode where a set number of spins are awarded at no additional cost to the player. Free-spins rounds typically include enhanced mechanics (multipliers, sticky wilds, expanded reels) and account for a significant portion of most games' RTP. Retriggers during free spins may add further spins. See: Free-spins multipliers guide.

G

Gamble feature

An optional mini-game offered after a win where the player can risk some or all of their win for a chance to multiply it (typically guess card colour for 2× or suit for 4×). Gambling the win adds an additional expected-value calculation: a 50/50 guess at 2× is EV-neutral; a 4-way guess at 4× is also neutral if fair. Not available in all markets.

Grid slot

A slot played on a non-standard grid shape (e.g. 5×5, 6×6, 7×7) rather than traditional 3–5 reels. Often uses cluster-pay mechanics and cascades.

H

High-value symbols

Symbols that pay more per winning combination than low-value symbols. Typically themed artwork specific to the game (characters, objects, etc.) rather than generic card symbols.

Hit frequency

The percentage of spins that result in any winning combination (however small). A 30% hit frequency means approximately 1 in 3 spins returns some win. A measure of how often wins occur — distinct from how large they are. Lower hit frequency generally signals higher volatility.

Hold percentage

The theoretical percentage of all wagered money that the game retains as operator revenue = (1 − RTP). A 96% RTP game has a 4% hold. Also called house edge or house margin.

House edge

See Hold percentage. The mathematical advantage the game holds over the player, expressed as a percentage of each wager. Equivalent to (1 − RTP).

I

InfiniReels

A proprietary mechanic by NetEnt where additional reels are added to the game grid when specific symbols land, potentially expanding the playing field (and win opportunities) indefinitely within a single spin.

J

Jackpot (fixed)

A top prize that is a set multiple of the bet or a fixed currency amount — it does not grow over time. Distinct from a progressive jackpot.

Jackpot (progressive)

A prize pool that grows as players contribute a fraction of each bet. When triggered (by a specific game event), the current jackpot amount is awarded. May be linked across multiple games or casinos (network progressive). The headline RTP of progressive games often includes the jackpot contribution — which is only captured by the winner. Base-game RTP excluding jackpot may be significantly lower.

K

KYC (Know Your Customer)

Regulatory verification procedures requiring casinos to confirm player identity, age (18+), and sometimes address. Required before large withdrawals and as part of anti-money laundering compliance. Standard in all major regulated markets.

L

Left-to-right

Win direction: matching symbols must appear consecutively starting from the leftmost reel. Most games pay left-to-right. Some also pay right-to-left (listed as "both ways" in the paytable).

Line bet

In multi-line games, the amount wagered per active payline. Total bet = line bet × number of active lines. In fixed-line games, total bet is set directly without a per-line concept.

Low-value symbols

Symbols with smaller paytable payouts — typically generic card-rank symbols (A, K, Q, J, 10, 9) or coloured shapes/gems. They appear more frequently on the reels than high-value symbols and provide lower wins when matched.

M

Max bet

The highest stake allowed on a given game. Some games offer a single "max bet" button that sets all parameters to their maximum. In some older-style games (less common online), certain jackpots are only available at max bet — always check the paytable.

Max win cap

The maximum payout from a single spin, expressed as a multiple of the stake. If a natural calculation would exceed this, the cap amount is paid and the excess is forfeited. Required to be disclosed in regulated markets. See: Max win guide.

Megaways

A licensed mechanic by Big Time Gaming (BTG) where each reel displays a random number of symbols per spin (typically 2–7), creating a dynamic way count up to 117,649 on a 6-reel game. Widely licensed to other studios. See: Megaways guide.

Multiplier

A factor applied to wins. A 3× multiplier triples the win amount. Multipliers appear on wild symbols, during free spins, through cascade accumulation, or via bonus game mechanics. Multiple multipliers typically multiply each other, not add.

N

Non-winning spin

A spin that produces no win at all. Also called a dead spin or zero-return spin.

Nudge

A mechanic (more common in land-based and traditional formats) where reels can shift up or down by one or more positions after a spin, potentially completing or improving a win. In some modern online games, nudge is the name for a symbol that moves down when it lands on a reel (e.g. xNudge wilds in Nolimit City games).

O

Operator

The entity that runs the online casino where you play. Distinct from the game studio (software provider). The operator holds a gaming licence, manages player accounts, handles deposits/withdrawals, and configures which games to offer (and at what RTP tier, where options exist).

P

Paytable

The in-game document specifying all symbol values, win conditions, special symbol rules, bonus mechanics, maximum win cap, and RTP. Required by regulation in most markets. Your primary reference for understanding a specific game. See: How to read a paytable.

Pay line

A predefined path across the reels. A winning combination must land exactly on a payline to count. Most modern online slots use ways to win rather than paylines, but paylines remain common in traditional-style games.

Pick game / pick bonus

A bonus round where the player selects from a set of hidden options (chests, doors, symbols) to reveal prizes. Prizes are pre-determined by the RNG; the player's "choice" does not affect outcomes in a mathematically meaningful way — all options lead to outcomes already generated by the game engine.

Progressive jackpot

See Jackpot (progressive).

Provably fair

A cryptographic method used mainly by crypto/blockchain casinos that allows players to independently verify each spin result using a published algorithm and seed. Contrasts with traditional RNG certification (third-party audit) by making verification available to the player directly.

R

RNG (Random Number Generator)

The algorithm that generates random outcomes for each spin. In certified licensed games, the RNG must pass independent testing. The RNG produces results statistically indistinguishable from true randomness and has no memory of past outcomes.

RTP (Return to Player)

The percentage of all money wagered that a game is designed to return to players over a very large number of spins. A 96% RTP game returns €96 per €100 wagered in aggregate, long-run. Not a per-session guarantee. See: RTP guide.

Respin

A spin triggered by the game (not paid separately by the player) as part of a feature — for example, after an expanding wild lands, the reel re-spins with the wild held in place. Typically free of charge and part of the game's normal mechanic.

Retrigger

Landing the scatter/trigger requirement again during a free-spins bonus round, extending the feature with additional free spins. May have a cap on the total spins achievable through retriggering.

S

Scatter symbol

A symbol that pays regardless of position — it doesn't need to be on a payline or adjacent reel. Typically triggers the bonus round when a minimum number (usually 3) appear anywhere on the reels simultaneously. May also award a direct payout.

Stake / bet

The amount of money wagered on a single spin. Also called total bet. All payout multiples are relative to this amount.

Sticky wild

A wild symbol that remains in position for one or more subsequent spins after landing, rather than disappearing after the initial win evaluation. Often triggers a respin.

Stacked symbol

A symbol appearing multiple times consecutively on a reel strip, so it may cover multiple visible positions on that reel in a single spin. Increases the probability of that symbol appearing on multiple rows simultaneously.

T

Tumble

Pragmatic Play's branding for the cascade/avalanche mechanic. See: Cascade.

Theoretical RTP

The RTP calculated through mathematical analysis of the game's complete probability distribution, verified by testing lab simulation. Equivalent to the published RTP figure. "Theoretical" distinguishes it from the actual RTP observed in a specific session (which varies due to variance).

U

Unlimited multiplier

A multiplier with no ceiling that can grow indefinitely during a cascade chain or free-spins session. The primary mathematical mechanism behind very high max-win caps in games like Megaways variants. Most sessions still produce modest multipliers; the extreme values are statistically rare.

V

Variance

See Volatility. The statistical spread of outcomes around the mean. Used interchangeably with volatility in common slot discussion.

Volatility

A description of how spread out a slot's payout distribution is. Low volatility: frequent small wins, tight distribution. High volatility: infrequent large wins, wide distribution. Same RTP can be delivered at any volatility level by adjusting payout frequency and size. See: Volatility guide.

W

Wagering requirement

A casino bonus condition requiring the player to wager the bonus (or deposit + bonus) a specified number of times before the balance is withdrawable. Important context for evaluating casino bonuses — the effective value of a bonus depends heavily on the wagering requirement and which games contribute.

Ways to win

A win structure where any matching symbols on consecutive adjacent reels (left to right) constitute a win, regardless of vertical position. The number of ways = product of symbols-per-reel for each reel. A 5×3 ways game has 3⁵ = 243 ways. See also: Megaways.

Wild symbol

A symbol that substitutes for most other symbols to complete or extend winning combinations. Specific substitution rules (what it replaces, whether it pays on its own, any multiplier it carries) are defined in the paytable.

Win cap

See Max win cap.

X

xNudge

A proprietary mechanic by Nolimit City where a wild symbol "nudges" (moves) down when it lands on a reel, filling the entire reel as a full-reel wild. Each position it nudges through increments the wild's multiplier. Distinctive to Nolimit City titles.

xWays

A Nolimit City mechanic where a symbol randomly reveals 2–4 symbols of the same kind, multiplying the effective way count for that reel position. Works within the game's win calculation to increase ways when these symbols land.