Slot pages throw around a lot of jargon — RTP, volatility, ways-to-win, Megaways — often without ever defining it. This slot glossary collects every term you’ll actually run into on a paytable or a review, grouped by what it describes rather than dumped alphabetically, so the maths terms sit together, the win-mechanic terms sit together, and so on. No invented numbers here — just the plain-English meaning of each one.
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Quick answers
What is RTP?
RTP (Return to Player) is the percentage of all money staked on a slot that the game is mathematically designed to pay back over millions of spins — a long-run average, not a promise for any single session. See our full what RTP actually means guide for the worked examples.
What does volatility mean?
Volatility (also called variance) describes how a slot pays, not how much. Low volatility means smaller wins that land often; high volatility means longer dry spells broken up by bigger hits. Neither is “better” — it’s a matter of which session shape you’d rather have.
The maths behind every game
RTP (Return to Player)
The theoretical percentage of every pound staked that a slot returns to players over the long run, tested and published by the studio. Read the full RTP explainer for how it’s actually calculated and why one session tells you almost nothing.
House edge
The mirror image of RTP — whatever percentage isn’t returned to players is the house edge. A 96% RTP game carries a 4% house edge; it’s the same number, viewed from the other side of the till.
Hit frequency
How often a spin lands any win at all, regardless of size. A slot can have a healthy RTP built from rare big wins and a low hit frequency, or frequent small wins and a higher hit frequency — two very different playing experiences that can share the same headline RTP.
Volatility (low, medium, high)
Sometimes badged variance instead. Low-volatility games smooth wins out over a session; high-volatility games concentrate the return into rarer, larger hits with longer waits between them; medium sits between the two. It’s the single most useful spec for predicting how a session will actually feel.
Max win
The largest possible payout on a single spin, expressed as a multiplier of your stake — for example a “10,000x max win” on a £1 stake caps out at £10,000. It’s a ceiling, not an expectation; the overwhelming majority of spins never come close.
Stake limit
The minimum and maximum bet the game (or your casino) allows per spin. UK-licensed online slots also carry regulator-set per-spin caps on top of whatever the game itself allows.
How wins are formed
Paylines vs ways-to-win
Paylines are fixed lines across the reels — match symbols along one of those exact lines and you win. Ways-to-win (often “243 ways” or “1,024 ways”) drops the fixed lines entirely: matching symbols on adjacent reels pay regardless of their row position, which is why ways-based games advertise such large win-line counts.
Cluster pays
A grid-based alternative to both of the above — symbols pay when a cluster of matching icons touch each other, rather than sitting in a line or an adjacent-reel path. See our cluster pays explainer for how the grid mechanic actually works.
Megaways
A licensed engine where the number of symbols per reel changes on every spin, so the total ways-to-win can swing into the tens of thousands. Our Megaways guide covers the mechanic and the games built on it.
Scatter symbol
A symbol that pays or triggers a feature (usually free spins) regardless of where it lands on the reels — it doesn’t need to sit on a payline or touch other matching symbols, just appear enough times on screen.
Wild symbol
A symbol that substitutes for most other symbols to help complete a winning combination, similar to a joker in cards. Wilds are the most common way a near-miss turns into a win.
Expanding wild
A wild that grows to cover an entire reel (or more) once it lands, rather than staying in its original single position — turning one lucky symbol into several stacked wilds at once.
Sticky wild
A wild that stays locked in place for multiple spins, typically during a bonus round, instead of disappearing after the spin it landed on. Stacking sticky wilds across a handful of free spins is a common route to a big multi-spin win.
Multiplier
A value that multiplies a win by a set amount — a 2x multiplier doubles the payout, a 10x multiplier makes it ten times bigger. Multipliers can be fixed, can climb through a bonus round, or can be attached to specific symbols.
Feature symbol
A dedicated symbol whose only job is to trigger a specific bonus feature (as opposed to a scatter, which usually triggers free spins specifically) — common on modern grid and cluster games with several stacked features.
Bonus features & reel mechanics
Free spins
A set number of spins played without staking your own balance, usually triggered by landing enough scatter symbols. Free spins often carry their own rules — added wilds, multipliers or a different reel set — that don’t apply to the base game.
Bonus round
Any distinct feature that takes you out of the base game, whether that’s free spins, a pick-and-click mini-game, or a wheel spin. “Bonus round” is the umbrella term; free spins are the most common specific example.
Bonus buy / feature buy
An option on some slots to pay a lump sum (often 50–100x your stake) to skip straight into the bonus round instead of waiting for it to trigger naturally. It isn’t available on GB-licensed sites — the option exists on the same games elsewhere, but UK operators remove it.
Respin
A single extra spin awarded mid-feature, usually with certain reels or symbols locked in place, that resets a small countdown each time it produces a fresh qualifying result. Hold and win-style features are built almost entirely out of respins.
Cascading / tumbling reels
Winning symbols disappear after they pay, and new symbols drop in to fill the gaps — so a single spin can chain several wins in a row, each one funded by the symbols the last win cleared out. Full breakdown in our cascading reels explainer.
Hold & win / hold & spin
A feature where landing enough of a special symbol locks the grid and awards a fixed number of respins; every extra special symbol that lands resets the respin count and adds to the prize, until the respins run out or the grid fills completely. See our hold and win guide for how the format spread across so many studios under different names.
Jackpots
Progressive jackpot
A prize pool that grows with every real-money bet placed on the game (or across a network of games) until someone triggers it. Our progressive jackpot guide untangles the networked, local and must-drop variants in detail.
Must-drop / daily jackpot
A progressive jackpot guaranteed to pay out by a deadline — typically before midnight, or once the pot reaches a set ceiling — rather than climbing indefinitely until it happens to trigger.
Playing the game
Autoplay
A setting that spins the reels automatically for a set number of rounds at your chosen stake, without you clicking spin each time. Most UK-licensed slots cap how many autoplay spins you can queue and add loss-limit stops.
Demo mode
A free-play version of a slot that uses virtual credits instead of real money, running on the same RTP and math model as the real-money game — the only reliable way to try a game’s feel before staking anything.
RNG (random number generator)
The certified algorithm that decides every spin’s outcome independently of any spin before or after it. It’s what makes a slot’s results fair and unpredictable, and it’s tested by independent labs before a game can be licensed for the UK market.
Paul edits Sister Slots’ UK slot-family guides. He researches provider histories, mechanics and published game data, checking material claims against provider sources and relevant public records. Unless a page states a dated hands-on method, it reflects documented editorial research rather than real-money play. More about Paul →