Reels
The vertical columns that spin when you press the button. Most slots have 3, 5, 6 or 7 reels.
Education
Slot Machine Terms Explained
A clear, jargon-free guide to modern slot terminology. Megaways, RTP, volatility, cluster pays, cascading reels, wilds, scatters and bonus buy — explained before you spin.
Published by
31Casino Editorial Team
Read time
12 min
Main topic
Slot mechanics & maths
Updated
May 2026
🎰
Free to play
Play Free Demo Slot Machines
Section 01
The basics: reels, paylines and ways to win
Every slot is built on the same foundation. Once you understand these terms, the more advanced mechanics covered later become much easier to follow.
Rows
The horizontal positions visible on each reel. A "5×3" slot has 5 reels with 3 visible symbols each.
Paylines
Fixed lines across the reels where matching symbols must land to form a winning combination.
Ways to Win
Any combination of matching symbols on adjacent reels (left to right) counts as a win — no fixed line needed.
Bet / Stake
The amount wagered per spin. On most slots the total stake is divided across all active paylines or ways.
Paytable
The information screen showing symbol values, special features, RTP and rules. Always worth reading before you play.
Quick orientation
"Paylines" and "Ways to Win" answer the same question — how does this slot decide what counts as a win? — in two different ways. A 25-payline slot wins on 25 specific patterns. A 243-ways slot wins on any matching symbols on adjacent reels, regardless of position on the reel.
Section 02
The numbers that matter: RTP, volatility, max win
These numbers describe how a game behaves over time. They matter more than theme, graphics, or feature count.
RTP — Return to Player
RTP is the theoretical percentage of all money wagered that a slot pays back to players over a very large number of spins. A 96% RTP returns 96 of every 100 units staked on average. This is a long-run statistical model, not a per-session guarantee.
High (player-friendly)
97.0%+
Industry average
95.0% – 96.5%
Below average — avoid
< 94.0%
Volatility (variance)
Volatility describes how a slot pays. Two games can share the same RTP and behave very differently in a single session.
| Volatility | Win frequency | Win size | Best suited for |
|---|---|---|---|
| Low | Frequent | Small | Long sessions on a small budget |
| Medium | Balanced | Mixed | General play |
| High | Rare | Large | Bonus-hunting, high loss tolerance |
Hit Frequency
How often the slot lands a winning spin of any size. Expressed as a percentage — 25% means roughly one in four spins returns something, no matter how small.
Max Win
The theoretical maximum payout, shown as a multiplier of your stake — e.g. 5,000× or 100,000×. High max wins almost always pair with extreme volatility.
House Edge
The mathematical inverse of RTP. A 96% RTP slot has a 4% house edge — the long-run advantage the operator holds from which profit and overhead are funded.
Reality check
RTP and volatility are statistical descriptions, not promises. A short session can deviate enormously from published numbers in either direction. The published RTP only becomes reliable across millions of spins combined — never within your individual play.
Section 03
Slot symbols: wilds, scatters, bonus and mystery
Beyond standard themed symbols, modern slots use a layer of special symbols that change how wins form or trigger features. This is where most provider-to-provider variation appears.
Wild symbols
Standard Wild
Substitutes for any regular symbol to help complete a winning combination.
Expanding Wild
Grows to cover an entire reel when it lands, dramatically increasing potential wins on that spin.
Sticky Wild
Stays in place across multiple spins or respins. Common in free-spin features.
Walking Wild
Moves one or more positions across the reels with each new spin or respin.
Stacked Wild
Multiple wild symbols stacked vertically on a single reel, increasing the chance of full-reel coverage.
Multiplier Wild
Substitutes and multiplies any win it contributes to, typically 2×, 3×, 5× or more.
Scatter symbols
Triggers for most bonus features. Scatter payouts and activations are independent of paylines — they pay or trigger wherever they land on the reels.
Bonus symbol
Some slots distinguish a scatter (for free spins) from a separate bonus symbol that triggers a different feature, such as a pick game or a hold-and-win round.
Mystery symbol
A placeholder that reveals itself as a regular symbol after the spin. All mystery symbols on the reels typically transform into the same revealed symbol, creating surprise wins.
Section 04
Win mechanics: how modern slots calculate wins
This is where the most innovation has happened in the last decade. Megaways, cluster pays and cascading reels have replaced fixed paylines on many of the most popular new releases.
Megaways
Dynamic reels with a variable number of symbols per spin. Most versions top out at 117,649 ways to win.
Originally created by Big Time Gaming. The number of symbols on each reel changes every spin, so the number of ways to win also changes constantly. The mechanic is now licensed to many other studios under various branded names.
Cascading Reels
Winning symbols disappear and new ones fall in — potentially creating multiple wins from a single paid spin.
Also marketed as "tumbling reels" or "avalanche." The same mechanic appears under all three names. Cascading reels are especially common in cluster-pays slots.
Cluster Pays
Wins form when a group of 5 or more matching symbols touch each other on a grid — not along paylines.
Almost always paired with cascading reels. When a cluster wins, those symbols disappear and new ones fall in, potentially creating a chain of wins from one bet.
All Ways / 243-4,096 Ways
Any matching symbols on adjacent reels from left to right form a win, regardless of position.
A simpler relative of Megaways: fixed symbols per reel, fixed ways to win. A 5-reel, 3-row all-ways slot gives 243 ways (3×3×3×3×3).
Hold and Win
Special money symbols lock in place while other reels respin, collecting values until the feature ends.
Also called "lock and respin." Each new money symbol that lands resets a counter, usually to 3 respins. The feature ends when the counter hits zero, paying out the total collected.
Expanding Reels
The reel size grows during a feature, adding more symbol positions and ways to win.
For example, 5 reels expanding from 3 rows to 6 rows in the bonus round. Often combined with Megaways or cascading reels.
Standard Megaways specs
| Max ways to win | 117,649 |
| Typical reel count | 6 reels + horizontal reel |
| Symbols per reel (varies) | 2 – 7 per spin |
| Mechanic origin | Big Time Gaming (licensed to many studios) |
Section 05
Bonus features: free spins, jackpots and more
Bonus features are where most of a slot's biggest wins come from. They're also where regulation differs most between markets.
Free Spins
A round of bonus spins triggered by 3 or more scatters. Usually includes extra features — multipliers, sticky wilds, or upgraded paylines.
Bonus Buy / Feature Buy
Pay 50–100× your stake to instantly enter the bonus round. Restricted or banned in the UK, Netherlands, and other regulated markets due to its higher-risk profile.
Pick Bonus
Choose from hidden options to reveal cash prizes, multipliers, or feature triggers. Outcome is pre-determined by the RNG at the moment the feature starts.
Wheel Bonus
A spinning wheel awards prizes, multipliers, or jackpot tier triggers when it stops.
Gamble Feature
An optional double-or-nothing round after a win — typically a 50/50 colour or higher/lower card guess. Banned in some markets.
Progressive Jackpot
A jackpot that grows from a tiny portion of every bet across all players on the network. Can reach seven or eight figures.
Fixed Jackpot
A jackpot with a set value that does not grow over time. Usually easier to trigger than a progressive.
Bonus buy availability
Bonus buys are restricted or banned in several regulated markets — including the United Kingdom and the Netherlands — because they shift the player's risk profile sharply. If a slot's bonus buy button is greyed out, that's a regulatory restriction, not a technical error. Regulators consider the feature higher-risk and have removed it locally.
Section 06
Provider terms: branded mechanics decoded
Each studio brands its own twist on a standard mechanic with a unique name, which can make slot lobbies feel more confusing than they need to be. Most are variations on what this guide has already covered.
| Branded name | What it actually is |
|---|---|
| Megaways (Big Time Gaming) | Dynamic reels with variable symbol counts |
| MegaClusters (Big Time Gaming) | Cluster pays on an expanding grid |
| Feature Drop | Bonus buy, often at multiple price tiers |
| Power Ways / Extra Ways | All-ways pays variant with stacked symbols |
| Tumble / Cascade / Avalanche | Three names for the same cascading-reels mechanic |
| Hold & Win (various) | Money-symbol respin with fixed respin counter |
| Win Exchange | Convert smaller wins into bigger feature triggers |
Useful rule of thumb
If a slot's marketing copy mentions a feature you've never heard of, check the paytable. Almost every "innovative" mechanic is one of the patterns above with new branding. Understanding the underlying mechanic tells you far more than knowing the branded name.
Section 07
How to read a slot before you play
The information you need lives on the slot's paytable and info screen. It takes about a minute to check, and it's the single most useful habit a slot player can develop.
1
RTP
Below 95%? Look elsewhere — there is no shortage of slots above 96%.
2
Volatility
Match it to your budget and patience, not your mood.
3
Max win
50,000× cap or higher usually means very long dry spells.
4
Features
Confirm which exist — free spins, multipliers, hold & win — and how they trigger.
5
Bonus buy cost
Note the price as a multiple of your stake before considering it.
6
Minimum bet in features
Some slots have surprisingly high minimums during bonus rounds.
7
Session budget
Set it before you start — not after the first losing spin.
A practical tip
If a slot is new to you, try the demo version first. Demo play costs nothing and shows you in a few minutes whether the volatility, pace and bonus frequency suit you — information no review or video preview can fully convey.
Frequently asked questions
What does Megaways mean in slots?
Megaways is a slot mechanic where the number of symbols on each reel changes from spin to spin. Because of this, the number of possible ways to win also changes every spin. Many Megaways slots go up to 117,649 ways to win. The mechanic was created by Big Time Gaming and is now licensed to many other studios.
What does RTP mean in slots?
RTP stands for Return to Player — the theoretical percentage of all money wagered on a slot that is paid back to players over a very long period. A 96% RTP means the slot returns 96 of every 100 units staked on average across millions of spins. It does not mean you personally will get back 96% in any single session.
What is volatility in a slot?
Volatility (sometimes called variance) describes how a slot tends to pay out. Low-volatility slots produce smaller wins more frequently. High-volatility slots pay out less often but those wins can be much larger. RTP and volatility are separate things — two slots can share the same RTP while feeling completely different in a session.
What are cascading reels?
Cascading reels — also called tumbling reels or avalanche — is a mechanic where winning symbols disappear after a win and new symbols fall down to take their place. A single paid spin can therefore produce several consecutive wins. Cascading reels are common in cluster-pays slots and modern grid-based games.
What is a bonus buy feature?
A bonus buy lets you pay an upfront amount — usually 50 to 100 times your stake — to instantly trigger the slot's bonus round instead of waiting for it to land naturally. Bonus buys are restricted or banned in several regulated markets, including the United Kingdom and the Netherlands, because of their higher-risk profile.
What is the difference between wilds and scatters?
A wild substitutes for other symbols to help complete winning combinations. A scatter triggers special features such as free spins or bonus rounds, and usually pays regardless of where it lands on the reels. A slot can have multiple wild types — expanding, sticky, walking — alongside a separate scatter or bonus symbol.
Keep reading
Guides that help you put the terminology you've just learned into practice.
Education
RTP explained in depth
Return to Player unpacked: what the number measures, where it helps, and where it misleads.
Education
Verify fair play at casinos
How testing labs, certifications and licences support the numbers you see on a slot's info screen.
Education
How game testing works
Independent labs test RTP and randomness — here is what that process actually involves.
Guide
Choose a casino safely
A practical checklist for evaluating licences, cashiers, support and responsible gambling tools.
Play with awareness
Slots are designed as entertainment, not as a way to make money. Set a budget before you play, stick to time limits, and never chase losses. If gambling has stopped feeling fun, free and confidential support is available — see our responsible gambling page or your country's local helpline via our country guides. 18+. Gambling can be addictive.
This guide is part of 31Casino's independent educational library. We don't take affiliate commissions on provider mentions and don't recommend specific casinos in this guide.