Betting Terms Glossary, in Plain English

By · author of the MIT-licensed teachersbettextbook library ·

The vocabulary behind the tools and the lessons: the terms you’ll meet on the board, in the Report Card, and anywhere bettors talk shop.

Each entry below opens with a definition that stands on its own, then the arithmetic that makes it concrete. Every term has its own link: click a heading, copy the URL, and it lands on that definition. Terms run roughly in the order the math does: from a posted price, through the vig, to a fair value, an edge, a stake, and the score afterwards.

Moneyline (American odds)
A moneyline is a bet price quoted in American odds, where a negative number is the stake needed to win $100 and a positive number is the profit on a $100 stake. So −150 means risking $150 to win $100, and +130 means a $100 stake wins $130. The sign tells you which side the market makes the favorite; the size tells you by how much.
Implied probability
Implied probability is the win chance a betting price corresponds to, before the bookmaker's margin is taken out. A moneyline of −150 implies 60%, because 150 ÷ (150 + 100) = 0.60. Add the implied probabilities of both sides of a market and the total lands above 100%; that excess is the vig.
Confidence (on a fair line)
How much evidence stands behind a pooled fair line. It is not a claim about whether the arithmetic is right, and not a probability that the bet wins. Three things move it: how closely the venues agree, how many independent venues there are (copycat feeds posting the same line collapse to one before this is counted), and whether a venue trusted to lead the pool is among them. A line pooled from no trusted venue is capped at 45% however tightly the rest agree. Two venues agreeing perfectly can therefore show tight agreement and a low confidence at the same time: that is agreement without much evidence behind it. The full formula is published.
Vig / juice
The vig, also called juice, is the bookmaker's built-in margin. It is why the implied probabilities of both sides of a market sum to more than 100%. A market priced −110 / −110 implies 52.38% a side, or 104.76% in total, so the market carries a 4.76% overround. A book's hold, its expected keep per dollar handled, is smaller than the overround: 4.76 ÷ 104.76 ≈ 4.5%. Stripping the vig out is the first step in every calculation on this site.
Overround
The overround is the amount by which the implied probabilities of every outcome in a market exceed 100%. A two-sided market implying 52.38% and 52.38% totals 104.76%, a 4.76% overround. It is the vig stated as a sum rather than as a fee, and it is what de-vigging removes.
De-vig
De-vigging is the arithmetic that strips a bookmaker's margin out of a two-sided price to recover the fair probabilities underneath. The simplest method is proportional: divide each side's implied probability by their total, so 52.38% and 52.38% become 50% and 50%. The power and Shin methods instead push more of the margin onto the longshot, which is where books load it. The no-vig calculator runs all three side by side, and the full de-vig guide shows the derivations.
Fair value / fair odds
Fair value is the price of an outcome once the bookmaker's margin has been removed: what the market actually believes, before the fee. A −110 / −110 market de-vigs proportionally to 50% a side, which is fair odds of +100 on both. Every edge on this site is measured against a fair price, never against a posted one.
Closing line
The closing line is the final price a market settles on immediately before the event starts. It is the sharpest public estimate of the true odds, because by then it has absorbed every injury report, lineup change and dollar of money that arrived beforehand.
CLV (closing line value)
Closing line value, or CLV, is the gap between the price you took and the de-vigged closing line on the same outcome. Taking +120 on a side that closes at a fair +100 is positive CLV: you got a better price than the market's own final estimate. CLV scores the price, never whether the bet won, which is why it converges on a far smaller sample than profit does. The closing line value calculator turns an entry price and a closing price into a gap in probability points, and the CLV guide explains why that number measures skill.
Sharp book
A sharp book is a sportsbook whose prices stay close to fair because it welcomes winning customers and moves its line on informed money. Its posted price is a usable estimate of the true probability, which is why sharp books get used as benchmarks rather than as places to hunt for mistakes.
Soft book
A soft book is a sportsbook that shades its prices toward public opinion and limits or closes accounts that win. Its lines drift away from fair value, and those gaps are where a price better than the true probability turns up.
Sharp consensus
A sharp consensus is a single fair line pooled from several sharp venues at once, rather than copied from any one book. Pooling in log-odds space and weighting each venue by how tight and how fresh its market is produces an estimate that survives one venue being wrong or stale. The sharp consensus fair line explains how the pool is built, and when it refuses to publish a number at all.
Edge
An edge is the gap between the true probability of an outcome and the probability the offered price implies. A price implying 45% on an outcome a fair line puts at 50% carries a five-percentage-point edge. That gap, not a hunch, is what expected value is computed from.
+EV (positive expected value)
A bet is positive expected value, or +EV, when the fair probability of the outcome is higher than the probability its price implies. Expected value per dollar staked is EV = p · b − (1 − p), where p is the fair win probability and b is the net profit on a winning dollar. A +EV price averages a profit over many repetitions no matter what any single bet does. The expected value calculator computes it from a fair line and your price, and prints $0 when the inputs contain no edge.
Kelly criterion
The Kelly criterion is the stake size that maximizes the long-run growth rate of a bankroll, given an edge and the odds on offer. For fair win probability p and net decimal profit b, the Kelly fraction is (b · p − q) / b, where q = 1 − p. Full Kelly is optimal only if p is exactly right, so a fraction of it (half by default here, a quarter when the edge is a guess) keeps most of the growth for far less volatility. The Kelly criterion calculator sizes a single bet; the Kelly guide derives the formula.
Bankroll
A bankroll is the money set aside for betting and nothing else. Kelly sizing is expressed as a fraction of it, so the bankroll is the denominator every stake is measured against, and it is re-measured after every settled bet.
Arbitrage (arb)
Arbitrage, or an arb, is backing every outcome of a market at different venues, at prices that return a profit whichever side lands. It exists when the implied probabilities of the best available prices sum to less than 100%. Arbs are real but rare and short-lived: many last seconds. Taking them repeatedly is the fastest route to a limited account. The arbitrage calculator checks the condition and splits a stake so both outcomes return the same, and arbs are flagged free on the live board rather than sold.
Limit / getting limited
Getting limited is a sportsbook cutting the maximum stake it will accept from an account, or closing the account outright, because it wins. It is the standard outcome for a consistently profitable customer at a soft book, and it is why closing line value, which a limited account still has, is a more durable measure of skill than a bankroll graph.
Line movement / steam
Line movement is the change in a market's price as money and news arrive between the opening line and the close. A move toward the side you already took is a positive signal about the price you got. Steam is the name for a fast, coordinated move across several books at once. A venue that moves before the others is said to have led the move.
Push
A push is a tie against the line: the result lands exactly on the number, the stake is returned, and the bet grades as neither a win nor a loss. Only whole-number lines can push. A half-point, like −3.5, removes the possibility entirely.
Parlay
A parlay is one bet that needs several outcomes to all land, paying the product of the individual prices. Multiplying prices multiplies the margin with them: three independent legs at −110 pay about +595, where three fair coin flips would pay +700. The ticket's hold is therefore far larger than any single leg's. The parlay calculator shows the combined price and the hold on it, and the betting-mistakes guide works through why the number climbs so fast.
Prediction market
A prediction market is an exchange where an event outcome trades as a contract that settles at $1 if it happens and $0 if it does not. The price is therefore a probability quoted in cents: a contract at 62¢ prices the event at 62%. Kalshi is a CFTC-regulated event-contract exchange available in the US; Polymarket and Betfair are restricted or unavailable to US users, and that status is an open legal question rather than a settled one.
Order book
An order book is the live list of resting buy and sell orders for a contract, with the size available at each price. The best bid and best ask bracket the market's price. The microprice weights the bid and ask by the size resting on the opposite side, so it leans toward the thinner side, the one about to get taken. That makes it a better fair-value estimate than the midpoint.
Kalshi trading fee
Kalshi's taker fee is 7% of the contract price multiplied by one minus that price, rounded up to the next cent per contract. It peaks at 1.75¢ a contract at a price of 50¢ and shrinks toward the tails: the opposite shape to sportsbook vig, which is heaviest on longshots. Entry and exit are both charged, so a round trip pays the fee twice while holding to settlement pays it once. The Kalshi fee calculator computes it for a given price and size.
Break-even price
A break-even price is the fair probability at which a position returns exactly zero once fees are paid. Buying a Kalshi contract at price P as a taker breaks even when the true probability is at least P + 0.07 × P × (1 − P), which at 50¢ is 51.75%. Fair value and break-even are different numbers, and this site reports them separately rather than blending them into one.