31 betting and tennis terms, each defined in one or two sentences, with the figure from our corpus where it exists.
Each definition has its anchor: a link to a term stays valid. Guide published on 05/09/2026.
A bet whose odds exceed the fair odds, 1 divided by the true probability. Its expected value is positive: EV = p × c − 1 > 0.
Decimal odds
What 1 € staked returns, stake included. Odds of 2.50 return 2.50 € for 1 € staked, i.e. 1.50 € net profit.
Implied probability
1 divided by the odds. Odds of 2.00 mean 50%. The sum of a match's implied probabilities exceeds 100% because of the margin.
Bookmaker's margin (overround)
The excess of the sum of implied probabilities above 100%. On our corpus since 2021 it averages 6.15% at opening.
Fair odds
1 divided by the true probability of the outcome. The threshold above which a bet has value.
Expected value (EV)
Average profit per euro staked over a large number of identical bets: p × c − 1, with p the probability and c the odds.
Opening odds
The first odds published on a match, often several days before the start.
Closing odds
The last odds before the match starts. They incorporate all available information and serve as the reference for measuring value.
CLV (closing line value)
The gap between the odds taken and the closing odds. Regularly beating the close is the best sign of a real edge.
Flat stake
Staking the same amount, or the same percentage of the starting bankroll, on every bet. The only way to read an ROI.
Martingale
Increasing the stake after a loss to recover it. It does not change the expected value and exposes the bankroll to ruin.
Kelly criterion
The fraction of the bankroll to stake to maximise its growth: (p × c − 1) / (c − 1). In practice, a fraction of Kelly (a quarter, a half) to limit variance.
ROI (return on investment)
Net profit divided by the total staked. +5%: 5 € won for 100 € staked.
Yield
Another name for ROI per bet, used by tipsters.
Drawdown
The largest loss between a bankroll peak and the trough that follows. The measure of the risk you will have to live through.
Variance
The spread of results around the expected value. At odds of 1.80, five losses in a row happen regularly without the model being bad.
Walk-forward validation
Predicting each season with a model trained only on the previous seasons. Training seasons are excluded from the measurement.
Calibration
A probability is calibrated if, across all matches announced at 60%, about 60% are won. Measured with the Brier score.
Favourite
The player with the lowest odds. On our corpus since 2021, the market favourite wins 68.8% of matches.
Outsider
The player with the highest odds. An underdog at 3.00 wins, on average, a little less than one match in three.
Head-to-head (H2H)
The history of direct meetings between two players.
Tie-break
The deciding game played at 6-6 in a set, written 7-6 in the score.
Retirement (ret.)
A match stopped through injury, written “ret.” in the score. The opponent is declared the winner.
Walkover (w.o.)
A match not played, one player withdrawing before the start. Bookmakers generally void the bets.
ATP / WTA ranking
A rolling total of the points won over 52 weeks, published every Monday.
Points
Awarded according to the tournament category and the round reached: 2,000 for a Grand Slam, 1,000 for a Masters 1000, 250 for an ATP 250.
Challenger
The second tier of the men's circuit, below the ATP Tour; the WTA 125 events are the women's equivalent.
Masters 1000 / WTA 1000
The tournaments just below the Grand Slams: nine a year for men, ten for women.
Grand Slam
The four majors: Australian Open, Roland-Garros, Wimbledon, US Open. The only men's tournaments played best of five sets.
Surface
Hard, clay, grass, indoor hard. Records differ by surface: a player can win 65% of matches on clay and 50% on hard.
ITF
The entry-level circuit (M15, M25, W15, W35...), outside the scope of our alerts.
Frequently asked questions
What is the difference between odds and a probability?
The odds are what 1 € staked returns; the probability is the chance that the outcome happens. They are linked through the bookmaker's margin: implied probability = 1 / odds, and the sum of a match's implied probabilities exceeds 100%.
What are closing odds?
The last odds published before the match starts. They incorporate the information available at that moment and serve as the reference: a bettor who regularly takes odds above the close has a measurable edge.
What is the ROI of a bet?
Net profit divided by the total staked. On 100 bets of 10 € returning 1,050 €, the ROI is +5%. It only makes sense with flat stakes and over hundreds of bets.