Sports Betting Glossary
The vocabulary of sharp, +EV betting — defined in plain English. If you can read this glossary and actually understand expected value, closing line value, and devigging, you already know more than most bettors. Each term links to the tool or guide that puts it to work.
Expected Value (+EV)
The average profit or loss a bet would produce if you placed it an infinite number of times. A bet is +EV (positive expected value) when your true probability of winning is higher than the probability implied by the price. Betting +EV is the only mathematically sustainable way to beat the sportsbooks over the long run.
How we find +EV →Devigging (No-Vig)
Removing the sportsbook’s built-in margin (the vig) from a market to estimate the "fair" probability of each outcome. Devigging a sharp book’s price gives you a benchmark to compare other books against and find +EV.
No-Vig Calculator →Vig (Juice)
The commission a sportsbook charges, baked into the odds. On a fair coin-flip market priced at -110 / -110, the vig is about 4.5% — that hold is the book’s edge and the reason most bettors lose long-term.
Closing Line Value (CLV)
Whether you bet a better price than where the market settled at game time. Consistently beating the closing line is the strongest single indicator that your betting process has a real edge, because the closing line is the sharpest price the market produces.
CLV explained →Implied Probability
The win probability a betting price implies. American odds of +150 imply 40%; -150 imply 60%. Converting odds to implied probability lets you compare a price against your model’s estimate.
Odds Converter →Fair Odds
The price that exactly reflects an outcome’s true probability, with no vig. If something hits 50% of the time, fair odds are +100. Any price longer than fair odds is +EV.
Kelly Criterion
A formula for the bet size that maximizes long-term bankroll growth given your edge and the odds. Most bettors use a fraction (e.g. quarter-Kelly) to reduce variance.
Kelly Calculator →Arbitrage (Arb)
Betting both sides of a market at different books where the prices guarantee a profit regardless of outcome. Rare, short-lived, and limit-prone, but risk-free when executed correctly.
Arbitrage Calculator →Hold
The sportsbook’s theoretical profit margin on a market, expressed as a percentage. A 2-way market with a 4.5% hold means the book keeps about $4.50 of every $100 wagered across both sides.
Player Prop
A bet on an individual player’s statistical performance — points, rebounds, strikeouts, shots on goal, etc. — rather than the game result. Props are where soft, slower-moving lines (and the most +EV) tend to live.
Player prop trends →Over / Under
A bet on whether a stat finishes above (Over) or below (Under) a posted line. A "points 24.5" prop pays the Over if the player scores 25+, the Under at 24 or fewer.
Push
A tie between the result and the line (e.g. a player scores exactly the listed number on a whole-number line). Pushes are graded as no-action and your stake is returned.
Unit
A standardized bet size, usually 1% of your bankroll. Tracking results in units instead of dollars lets you compare performance independent of bankroll size.
Bankroll
The total money you’ve set aside specifically for betting. Disciplined bankroll management — flat or fractional-Kelly sizing — is what keeps variance from busting a profitable bettor.
Steam Move
A sudden, sharp, league-wide line movement caused by a wave of professional money hitting a market at once. Following steam after the line has already moved usually means you missed the value.
Line Movement
How a betting line changes from open to close as money comes in and books adjust. The direction and timing of movement is a key signal for where the sharp side is.
Middling
Betting both sides of a market at different lines so that a result landing in the gap (the "middle") wins both bets. A low-risk way to exploit line movement.
Betting calculators →Calibration
How closely a model’s stated probabilities match reality. A well-calibrated model that says "60%" wins about 60% of the time. Calibration — not just accuracy — is what separates an honest probability from a confident-sounding guess.
How we calibrate →Hit Rate
The share of graded bets that won. Useful, but on its own it can mislead — a 55% hit rate at -200 odds loses money, while 48% at +120 wins. Always read hit rate alongside price and ROI.
Prop Hit Rate tool →ROI
Return on investment — net profit divided by total amount wagered. The truest measure of betting performance, because it accounts for both win rate and the prices you got.
Our public ROI →Parlay
A single bet combining multiple legs that all must win. Parlays multiply odds — and multiply the vig — so standard parlays are usually -EV unless every leg is independently +EV.
Parlay Calculator →Alternate Line
A version of a market at a different number than the main line, with adjusted odds (e.g. taking a points Over at a lower line for a worse price). Useful for finding +EV the main line doesn’t offer.
NRFI / YRFI
No Run First Inning / Yes Run First Inning — a baseball bet on whether either team scores in the opening inning. A popular first-inning prop market.
NRFI strategy →Put the terms to work
Free calculators for no-vig, parlays, Kelly, and arbitrage — plus today's +EV picks across 48 books.