Casino Glossary — 25 Key Terms Defined

Casino gambling has its own vocabulary, and knowing it prevents confusion at the table and in strategy guides. These are the 25 terms you will encounter most often — defined precisely and without jargon.

Basic and structural terms

House edge. The casino’s mathematical advantage over the player, expressed as a percentage of each wager. A 2.78% house edge means the casino expects to keep $2.78 for every $100 wagered over a large number of bets. It is not a guarantee per session — short-term results vary widely — but it is mathematically certain over time.

RTP (Return to Player). The inverse of the house edge, expressed as a percentage of bets returned to players over the long run. A game with a 97% RTP has a 3% house edge. House edge = 100% − RTP.

Variance / Volatility. A measure of how much actual results swing around the mathematical expectation. High-variance games (slots, specific triple bets in Sic Bo) can produce large wins and large losses even though the long-run average is predictable. Low-variance games (baccarat, blackjack) produce results closer to the expected value in the short run. Variance does not change the house edge.

Bankroll. The total amount of money a player has set aside specifically for gambling. Proper bankroll management means sizing individual bets as a small fraction of your bankroll — typically 1–5% — to survive the inevitable losing runs that variance produces.

Session. A defined period of play with a set start and end point. Thinking in sessions — with a budget and a stop-loss limit set in advance — is one of the most practical tools for responsible gambling.

Comp. Short for complimentary. Casinos award comps (free meals, hotel rooms, credits, cashback) to players based on the volume and size of their action. Comps are funded out of the house edge on your play; they do not represent a net gain to the player in mathematical terms.

Probability and math terms

Expected value (EV). The average outcome of a bet if it were repeated an infinite number of times. In a negative-EV game (every standard casino bet), the expected value is negative for the player. EV = (probability of win × win amount) − (probability of loss × loss amount).

Standard deviation. A statistical measure of how spread out results are around the expected value. One standard deviation covers roughly 68% of outcomes; two standard deviations cover roughly 95%. High standard deviation means results can deviate significantly from EV in any given session.

Gambler’s fallacy. The false belief that past results in a game of independent trials influence future outcomes. A roulette wheel that has hit red eight times in a row is no more or less likely to hit black on the next spin. Each spin is independent. No number is “due.”

Independent events. Events where the outcome of one trial has no effect on any other trial. Dice rolls, roulette spins, and card shuffles (with replacement or after a full shuffle) are independent. Understanding this is the antidote to the gambler’s fallacy.

Kelly criterion. A formula for determining the mathematically optimal bet size when you have a known edge: bet a fraction of your bankroll equal to your edge divided by the odds. In casino play — where every standard bet has a negative edge — the Kelly criterion recommends betting zero. It is most relevant in sports betting or advantage play situations where a genuine positive edge exists.

Card game terms

Natural. An automatic high-value hand requiring no further cards. In blackjack, a natural is an ace plus any ten-value card, paying 3:2. In baccarat, a natural is a two-card hand totalling 8 or 9. In craps, a natural is a come-out roll of 7 or 11.

Push. A tie between the player and the dealer, resulting in the original bet being returned with no win and no loss. Common in blackjack (player and dealer have the same total) and baccarat (the tie bet being a separate wager rather than a push on banker/player bets).

Basic strategy. In blackjack, the mathematically optimal play for every possible combination of player hand and dealer upcard — derived from probability analysis of all possible card distributions. Playing perfect basic strategy reduces the blackjack house edge to approximately 0.5%.

Free odds. In craps, an additional bet placed behind a pass line, don’t pass, come, or don’t come bet once a point is established. Pays at true mathematical odds with zero house edge — the only standard casino bet with no house advantage. Taking maximum free odds is the single most effective way to reduce the house edge in craps.

Come-out roll. The first roll in a new craps round, before a point has been established. A come-out roll of 7 or 11 is a natural (pass line wins); 2, 3, or 12 is craps (pass line loses); any other number establishes the point.

Technology and format terms

RNG (Random Number Generator). Software used in online casino games to produce statistically random outcomes. A certified RNG ensures that digital dice, cards, and slots are equivalent to physically random versions. Reputable online casinos have their RNGs independently tested and certified by third-party auditors.

Progressive jackpot. A jackpot that accumulates across multiple rounds or machines, growing until one player wins it. Progressive jackpots typically come with a higher house edge built into the base game to fund the jackpot pool. The large headline figure is funded by a reduction in the base RTP.

Payline. In slot machines, a line across the reels along which matching symbols must land to produce a win. Modern video slots can have anywhere from 1 to hundreds of paylines, and the bet per payline structure significantly affects how the RTP is realised in practice.

Behaviour and risk terms

Hot / cold (myth). The belief that a machine, table, or dice is in a “hot” (winning) or “cold” (losing) streak that will continue. No such property exists in games of independent random outcomes. A slot that has not paid in 200 spins is no more likely to pay on spin 201.

Degenerate gambler (myth of the type). A common shorthand for problem gamblers that can obscure the reality of gambling disorder, which exists on a spectrum and is not a moral failing but a behavioural health condition. Responsible gambling resources are available through organisations like Stödlinjen (Sweden) and GamCare (UK).

Chasing losses. Increasing bet sizes or extending a session specifically to recover money already lost. This is one of the most consistent warning signs of problem gambling and mathematically worsens expected outcomes by increasing total exposure to the house edge.

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For the mathematics behind these terms, see Probability Basics. For a comparison of house edges across all major games, see Casino House Edge Explained.