What exactly is Marriott's definition of a "Convention Hotel?" According to the terms of service, Platinum and Gold Marriott elite members are entitled to guaranteed 4PM checkout at most types of hotels. Specifically excluded are "resorts and convention hotels." What makes a hotel a convention hotel? Is this any hotel that has a ballroom? Is this any hotel that has an attached convention center? Is this any hotel that is nearby independent convention centers? Without definition there is no way to know when a hotel may opt out of this "guarantee," which makes it not a guarantee at all.