Casino Glossary
A Working Glossary of Slot & Roulette Terms
Every term below appears somewhere in our slot guides or roulette coverage. Bookmark this page as a reference while you read.
Bonus Round
A separate feature triggered by a specific symbol combination (often three or more scatters) that plays out differently from the base game — free spins, a pick-and-win screen, or a multiplier chain.
Bonus Buy
A feature, offered by some studios, letting a player pay a fixed multiple of their stake to enter a bonus round directly instead of triggering it through normal play. Not available on every game or in every region.
Cascading Reels
Also called “tumbling reels” or “avalanche” mechanics — winning symbols disappear after a win, new symbols drop in to fill the gaps, and the process repeats as long as new wins keep forming from a single spin.
Cluster Pays
A payout system that removes fixed paylines entirely. Wins are formed by clusters of matching symbols touching each other (usually 5+ in a group), anywhere on the grid.
Double Zero
The extra “00” pocket found on an American roulette wheel, alongside the single “0.” It raises the wheel’s house edge from 2.70% to 5.26% compared with a European wheel.
Free Spins
A set number of spins awarded (typically by scatter symbols) that play automatically without using the player’s own stake, often with an added multiplier or expanded symbol set.
House Edge
The mathematical advantage a game holds over the player, expressed as a percentage, built into the rules themselves rather than any individual outcome. It’s the inverse of RTP for a given bet.
Inside Bet
In roulette, a wager placed on a specific number or small group of numbers within the numbered grid (straight-up, split, street, corner). Higher payout, lower probability.
La Partage
A French roulette rule that returns half of an even-money outside bet if the ball lands on zero, lowering the effective house edge on those bets to about 1.35%.
Megaways
A licensed mechanic that varies the number of symbols on each reel every spin, producing up to 100,000+ possible ways to win on a single spin instead of a fixed number of paylines.
Multiplier
A value that multiplies a win by a set amount (2x, 5x, 100x), often appearing during bonus rounds or cascading-win sequences and sometimes increasing with each consecutive win.
Outside Bet
In roulette, a wager placed on a broad category outside the numbered grid — red/black, odd/even, high/low, or a column/dozen. Lower payout, higher probability of hitting.
Paylines
The fixed patterns across a slot’s reels that a matching symbol combination must land on to form a win, running left to right in classic slot design.
Progressive Jackpot
A jackpot that grows continuously as a small percentage of every wager placed on a linked game (or network of games) is added to the pool, until a triggering combination pays it out.
Provider / Studio
The game-development company that designs and builds a slot or table game (e.g., Pragmatic Play, NetEnt, Play’n GO), as distinct from the casino operator that offers it to players.
RNG (Random Number Generator)
The certified algorithm that determines a game’s outcome the instant it’s triggered, independent of any previous or future result — the mechanic that makes outcomes statistically random rather than patterned.
RTP (Return to Player)
The percentage of all wagers on a game that it’s mathematically designed to pay back over a very large number of spins — a long-run average, not a per-session guarantee.
Scatter Symbol
A symbol that typically triggers a bonus feature (often free spins) when a set number appear anywhere on the grid, regardless of payline position.
Single Zero
The one “0” pocket on a European roulette wheel (37 pockets total), giving it a lower house edge (2.70%) than the American double-zero wheel (5.26%).
Slot Machine Games
The umbrella term for reel-based casino games, from mechanical three-reel originals to modern video slots with Megaways, Cluster Pays, and multi-stage bonus rounds.
Straight-Up Bet
A roulette wager on a single number, the highest-paying inside bet at 35:1, reflecting its low probability of hitting on any given spin.
Theoretical Return
Another name for RTP — “theoretical” because it describes the mathematical model behind the game, realized only over a very large number of spins.
Variance
A near-synonym for volatility — the statistical measure of how much a game’s individual results swing above or below its average return.
Volatility
How a game distributes its wins over time: low volatility means frequent, small wins; high volatility means rarer but potentially larger wins, at the same or a different RTP.
Wild Symbol
A symbol that substitutes for most other symbols on the grid to help complete a winning combination, sometimes carrying its own multiplier.
Wheel Format
The three main roulette layouts — European (single zero), American (double zero), and French (single zero plus rules like La Partage) — each with a different house edge. See our Roulette section for the full breakdown.
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