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Glossary

Roulette glossary – 50 essential terms, no fluff.

The language of roulette, systems and risk in plain English.

This glossary is your reference for everything mentioned across the site – from European vs American wheels to inside bets, house edge, volatility and popular systems like Martingale, Fibonacci and Labouchere. Each term is written for real players: short, clear and grounded in math, not mystique.

Use it alongside the How roulette works hub, the systems library and the Roulette Probability Calculator whenever you want to double-check what a concept really means.

🎡 Wheels & layouts 🎯 Bet types & payouts 📊 Odds, RTP & house edge 🧠 Systems & bankroll terms

A–Z roulette definitions

Terms are listed alphabetically. Where relevant, you’ll see links to deeper explanations in the Learn roulette hub, the systems library and the Probability Calculator.

American roulette
A roulette wheel with 38 pockets: numbers 1–36 plus 0 and 00. The extra green double-zero pocket increases the house edge (around 5.26% on most bets), making it less favourable than European roulette.
Bankroll
The total amount of money you set aside for gambling. A healthy bankroll is money you can afford to lose without affecting bills, savings or obligations.
Bankroll management
The practice of sizing bets and setting limits so your bankroll is not wiped out too quickly. It typically involves choosing a small betting unit, setting stop-loss and stop-win points, and avoiding chasing losses.
Betting unit
The basic bet size you use in a session or system (for example, $5 per unit). Many systems, including Martingale and Fibonacci, are defined in terms of units instead of currency.
Betting progression
Any rule that changes your stake size after wins or losses. Negative progressions increase bets after losses; positive progressions increase bets after wins. See Negative progression and Positive progression.
Black bet
An even-money outside bet on all black numbers on the wheel. On European wheels, black covers 18 of 37 pockets; on American wheels, 18 of 38. The green pockets (0 and possibly 00) create the house edge.
Column bet
An outside bet on one of the three vertical columns of numbers on the layout, covering 12 numbers. Standard payout is 2 to 1. The exact probability depends on the wheel type and can be analysed with the Probability Calculator.
Corner bet (square)
An inside bet that covers four numbers forming a square on the layout (for example, 17-18-20-21). Standard payout is 8 to 1. Higher variance than outside bets but less extreme than straight-up numbers.
Dozen bet
An outside bet on 12 numbers at once: 1–12, 13–24 or 25–36. Standard payout is 2 to 1. Dozens strike a balance between frequency (more hits than inside bets) and payout.
Double zero (00)
The extra green pocket on American roulette wheels. It increases the number of losing outcomes for most bets without raising payouts, roughly doubling the house edge compared with European roulette.
En prison rule
A European rule sometimes applied to even-money bets. If the ball lands on 0, instead of losing immediately, your stake is “imprisoned” for the next spin. Depending on the variant, you may recover your stake if the next spin wins. This slightly improves the effective house edge.
Even-money bet
Any bet that pays 1 to 1, such as red/black, odd/even or high/low. These bets hit relatively often but still have a built-in house edge because of the green pockets.
European roulette
A roulette wheel with 37 pockets: numbers 1–36 plus a single green 0. The house edge on standard bets is roughly 2.7%, lower than American roulette and usually preferable for players.
Expected value (EV)
The long-run average result of a bet, expressed per unit staked. It combines win probability, loss probability and payout. In roulette, EV is negative for all standard bets. The Probability Calculator shows EV for different bet types.
Flat betting
A betting approach where you wager the same stake on every spin, regardless of wins or losses. Flat betting does not change the house edge but usually reduces volatility compared with aggressive progressions.
Green zero
The single green pocket labelled 0 on European wheels and one of the two green pockets (0 and 00) on American wheels. Green pockets are the core reason even-money bets are not truly 50/50.
High / low bet
An even-money outside bet on either low numbers (1–18) or high numbers (19–36). As with other even-money bets, the green pockets make the odds slightly worse than 50/50.
House edge
The average percentage of each bet that the casino keeps over the long run. It is the negative of expected value expressed as a percentage. Systems can change volatility but not the underlying house edge of the game.
Inside bet
Any bet placed on the numbered grid itself: straight-up, split, street, corner or line bets. Inside bets pay more but hit less often, creating higher volatility.
Outside bet
Any bet placed in the boxes surrounding the grid: red/black, odd/even, high/low, dozens or columns. Outside bets hit more frequently but pay less than inside bets.
La partage rule
A European rule on some tables where half of an even-money stake is returned to the player if the ball lands on 0. This improves the effective house edge compared with standard rules, especially for even-money bets.
Line bet (six-line)
An inside bet covering six numbers across two adjacent streets (for example, 10-11-12 and 13-14-15). Standard payout is 5 to 1.
Martingale system
A classic negative progression system for even-money bets where you double your stake after each loss until a win, then reset to your original unit. It produces many small wins but exposes you to occasional very large losses when a long losing streak hits. See the Martingale guide.
Fibonacci system
A negative progression based on the Fibonacci sequence (1, 1, 2, 3, 5, 8, …). Stakes move forward after losses and backward after wins. It grows more slowly than Martingale but still increases stakes during losing runs. See the Fibonacci guide.
Labouchere system
A sequence-based negative progression where you write down a line of numbers, bet the sum of the first and last, cross numbers off after wins and add numbers after losses. It offers flexibility but can inflate stakes aggressively during bad runs. See the Labouchere guide.
D’Alembert system
A gentler negative progression where you increase your stake by one unit after a loss and decrease it by one unit after a win. It smooths swings compared with Martingale but still cannot change the house edge.
Oscar’s Grind
A positive progression system aiming for small, steady profits on even-money bets. You usually increase stakes after wins (within limits) and keep them flat after losses, trying to grind out a unit or two per series.
1-3-2-6 system
A short-cycle positive progression, often used over four spins on even-money bets. If you win, you move along the sequence 1, 3, 2, 6; if you lose at any point, you usually reset to 1. Designed to press winning streaks while capping risk in short sessions.
Negative progression
Any betting scheme where you increase your stake after a loss. Martingale, Fibonacci and Labouchere are all negative progression systems. They seek to recover losses with larger future bets but can lead to very large stakes when losing streaks occur.
Positive progression
Any betting scheme where you increase your stake after a win. Systems like Oscar’s Grind and 1-3-2-6 are positive progressions. They attempt to press hot streaks and reduce exposure during losing spells.
Probability
The mathematical chance that an event will happen, usually expressed as a fraction, decimal or percentage. In roulette, probability is determined by how many pockets count as a win versus the total number of pockets. The Probability Calculator makes this explicit for each bet type.
Payout odds
The advertised return for a winning bet, such as 35 to 1 on a straight-up number or 1 to 1 on an even-money bet. Payout odds are slightly worse than fair odds, and the gap is where the house edge comes from.
Red bet
An even-money outside bet on all red numbers on the wheel. Like black, it covers 18 numbers, but the green pockets (0 and possibly 00) give the house a small built-in edge.
Risk of ruin
The probability that your bankroll will eventually be wiped out (or fall to a defined loss threshold) if you continue betting under a particular system or stake size. Negative progressions often have a higher risk of ruin because stakes grow quickly during bad runs.
Roulette wheel
The physical (or virtual) wheel that the ball spins around. Its number of pockets and layout – 37 for European, 38 for American – determine the base probabilities of every roulette bet.
Session
A defined period of play, such as 30 minutes or 100 spins, with its own bankroll and goals. Many responsible gambling plans emphasise playing in clearly defined sessions instead of open-ended “until I’m back even” play.
Split bet
An inside bet on two adjacent numbers sharing a common border on the layout (for example, 17-20). Standard payout is 17 to 1.
Street bet
An inside bet covering three numbers in a horizontal row (for example, 1-2-3 or 31-32-33). Standard payout is 11 to 1.
Straight-up bet
An inside bet on a single specific number. Standard payout is 35 to 1. Straight-up bets offer the highest payout among standard bets but hit the least often.
Table limit
The minimum and maximum stakes allowed on a particular table or bet type. Table limits are a practical constraint that cause many progression systems, such as Martingale, to fail in real play long before “infinite bankroll” assumptions would.
Volatility
A measure of how wild the swings in your bankroll are. High-volatility play produces larger, less frequent wins and deeper drawdowns. Low-volatility play produces smaller, more frequent changes. Systems mainly change volatility, not house edge.
Zero pocket
The green 0 on European wheels and the green 0 and 00 on American wheels. These pockets are the main source of house edge on even-money and many other bets, since they tilt the odds without changing payouts.
RNG roulette
Online roulette games where outcomes are generated by a Random Number Generator rather than a physical wheel. Properly licensed RNG roulette should be audited so that the distribution of results matches the advertised rules.
Live dealer roulette
Online roulette streamed from a real table with a human dealer spinning a physical wheel. Bets are placed digitally, but the underlying game is physical, not RNG.
Stop-loss
A pre-defined loss limit at which you end a session, regardless of how the last few spins went. Stop-losses are a key part of responsible bankroll management and help prevent chasing losses.
Stop-win / win goal
A pre-defined profit target at which you stop playing for the session. Combined with a stop-loss, a win goal keeps sessions finite and helps prevent giving back all profits during extended play.
Tilt
A mental state where frustration, anger or excitement leads to irrational decisions – such as increasing stakes recklessly or abandoning limits. Tilt is one of the biggest risks in gambling, regardless of the system used.
Return to player (RTP)
The long-run percentage of total stakes that is theoretically returned to players. In a game with a 2.7% house edge, the RTP is 97.3%. RTP and house edge are two sides of the same coin.
Comps
Complimentary rewards (meals, rooms, cashback, etc.) offered by casinos based on your play. Comps partly offset the cost of gambling but do not turn a negative expectation game into a profitable one.
Stake
The amount of money you wager on a single spin or bet. In many tools and guides on this site, stake size is separated from probability so you can see both percentages and dollar expectations clearly.

Using this glossary with the rest of the site

Whenever a term in a system guide or tool feels fuzzy, jump back here, clarify the definition, and then revisit the math with a clearer head. Combined with the How roulette works hub, the systems library, the Probability Calculator and the responsible gambling page, this glossary is meant to keep your understanding grounded, not mystical.