An app is a program for mobile devices; an online sportsbook is accessible via a browser. We use the terms interchangeably as a shortcut, but that may be a bit misleading. It is possible that some sportsbooks will have different versions of their offerings on the two formats. In some cases, the app will be a pared-down version of the site. In others, there won’t even be a site — the entire sportsbook exists as an app.