This is a place where bets can be made on sporting events. Betting on sports is illegal in most US states, but has proliferated in the online marketplace and in select locations, such as Las Vegas.
Many casinos have a sports book within their walls, but a majority of gambling on sports is done via the internet. There are also many illegal sportsbooks that exist throughout the country. These illicit venues operate through private networks and as such, regulate themselves through violence, extortion, or more commonly, by refusing to take bets. A sports book will often have all the active games available to bet with betting lines displayed prominently for all to see. The casinos offer comfortable surroundings, HD televisions, and many other amenities in their sportsbooks. The term comes from the actual notebook that those receiving the bets and making the lines would use to keep track of bettors.