The term 'book' is a reference to the books used by wage brokers to track wagers, payouts, and debts. Sports bettors place their wagers either legally, through a bookmaker/sportsbook, or illegally through privately run enterprises referred to as 'bookies'.
Sports betting is the activity of predicting sports results and placing a wager on the outcome. Please help improve it to make it understandable to non-experts, without removing the technical details. This article may be too technical for most readers to understand.