What is a book / sportsbook in sports betting?

What is a book / sportsbook in sports betting? The company or establishment that accepts bets. In plain terms: the book is the house — it posts the prices, takes both sides, and keeps a cut either way. Every number you see starts at a book. “It's a whole new world, son — ten years ago everyone had a local book.” Let's use this example. The same game can sit at different prices at different books: Book A posts Kansas City minus six and a half, Book B posts minus seven. Same game, different number — which is exactly why line shopping exists. And one thing separates real books from the Slow-Pay Donnies of the world: real books pay winners, every time, without a phone call. Ask about the payouts before you ask about the prices. Lines and prices can differ by sportsbook. Nothing here guarantees a result or tells you to bet. Lines move and books differ. Nothing here is a guarantee or a command to bet — it's how the number works.