What is Betting exchange, back bet, lay bet, in-play betting?

A betting exchange is a venue on which bettors trade bets with each other through an order book and the operator charges a commission rather than taking positions. A back bet is a bet that an outcome happens; a lay bet is a bet that it does not, the layer taking the role of the bookmaker for that bet. In-play betting is betting while the event is under way, at prices that move with it.