They referred to such schemas like "FlightReservation"[1] for flights, "EventReservation"[2] commonly used for movie tickets, or "LodgingReservation" used for hotel bookings. The specific supporting website encodes your reservation in these formats inside the confirmation email, and Gmail picks up on that. (IIRC it used to scrape emails for that data, but most of it if not all is done via schemas nowadays)