Betting Exchange
A peer-to-peer marketplace where bettors wager against each other by backing and laying outcomes, with the operator taking a commission instead of building in a margin.
Definition
A betting exchange matches bettors who want to back an outcome (bet it will happen) with those who want to lay it (bet it will not), so users effectively set the odds among themselves rather than taking a bookmaker's price. The exchange earns money by charging a commission (commonly around 2 to 5%) on net winnings rather than by baking a margin into the odds, which is why exchange prices are often closer to fair value. Liquidity, meaning how much money is available at each price, determines how big a bet you can get matched.
Worked example
On an exchange you back Team A at 3.0 for $100, matched by another user laying it. If A wins you profit $200 minus, say, 5% commission ($10) for $190 net; if A loses you forfeit your $100.
Why it matters
Exchanges show learners that odds are ultimately a market, and they let advanced bettors lay outcomes, trade positions, and get closer-to-fair prices than traditional books offer.