Reference
Glossary
The vocabulary used across this desk, defined once and linked back to the page that works each idea out in full.
Terms A to E
Bankroll
The money set aside for play, treated as a fixed and finite quantity rather than something that replenishes.
Combination
A selection where order does not matter. Draw games are counted with combinations, not permutations. See lottery combinatorics.
Commitment scheme
A method of publishing a sealed record of a generated value before play, so it can be checked afterwards. See randomness.
Conditional probability
The probability of an event given that something else has already happened. It matters at a card table and not at a wheel.
Dependent trial
A trial whose probabilities are changed by what happened before it, as in cards dealt from a shoe without replacement. See cards.
Edge
The share of each unit staked that the rules retain on average. See house edge.
Entropy source
A physical process used to supply an unpredictable seed, in place of anything an observer could guess.
Expected value
The average result of a wager per unit staked, computed by weighting every outcome by its probability.
Terms F to L
Fair game
A game whose expected value is exactly zero. Free odds at a dice table are the standard example.
Free odds
A supplementary dice wager paid at true odds, and therefore carrying no edge of its own.
Gambler's fallacy
The belief that an independent trial is due to correct a run. A wheel has no memory.
Hold
The proportion of money brought to a table that the table retains over a session. Hold and edge are different quantities.
House edge
See edge. The figure is a property of the rules, not of any venue.
Independent trial
A trial whose probabilities are unaffected by earlier trials, as with dice and wheels.
Insurable interest
The requirement that a party stands to suffer a real loss, which is what separated insurance from wagering. See history of betting.
Jackpot pool
The accumulated fund from which a draw game's top prize is paid, as distinct from a fixed payout.
Law of large numbers
The result that the average outcome per round converges on its expected value as rounds accumulate. See the law of large numbers.
Licence condition
A term attached to a permission to operate, revocable rather than criminal, and the main instrument of modern regulation.
Terms M to R
Margin
The excess above one that a set of quoted prices sums to. It is the bookmaking equivalent of a house edge.
Odds against
A ratio expressing losing cases to winning cases, written as 36 to 1 rather than as a probability.
Over-round
A book of prices whose implied probabilities total more than one, which is what makes the book commercial.
Par sheet
The internal document that records a machine's symbol weighting and its resulting return. See machine design.
Payout odds
What the rules pay a winning wager, as distinct from the true odds against it winning.
Period
The number of values a pseudorandom generator produces before it repeats. See randomness.
Probability
A number between zero and one giving the proportion of cases in which an outcome occurs.
Problem of points
The question of how to divide a stake in an abandoned game, whose solution produced the idea of expectation.
Return to player
One minus the edge, expressed as a percentage of everything staked.
Rollover
A draw in which an unwon top prize is added to the next draw's pool, changing that draw's expected value.
Ruin
The state of having no bankroll left. Its probability rises with the edge and with the number of rounds played.
Terms S to Z
Sample space
The complete list of equally likely outcomes of a trial. Two dice have thirty-six.
Seed
The starting value that determines the whole sequence a pseudorandom generator will produce.
Shoe
The container from which several combined decks are dealt, used to dilute the effect of any one card's removal.
Stake
The amount risked on one round. Edge percentages are always expressed as a share of everything staked.
Standard deviation
A measure of typical distance from the expected result, growing with the square root of the rounds played.
Testing laboratory
An organisation independent of operator and manufacturer that examines a game's design documents before it is approved for use.
True odds
The real ratio of losing to winning cases, computed from the sample space.
Variance
The squared spread of results. High variance means long runs in both directions around the same expectation.
Virtual reel
A mapping that assigns each physical reel position a number of internal stops, so displayed symbols are not equally likely.
Volatility
The practical name for variance in machine design: how concentrated a return is in rare outcomes.
Zero pocket
The pocket or pockets on a wheel that belong to no even-money proposition, and that create the edge.