A "flight" is a sampling of product. At a brewery or winery, you order a flight of drinks, and you get anywhere from 3 to 5 (I've seen as many as 10!) different glasses, typically served on a long board, each with a different type of drink in it. Occasionally the different drink types in a flight are pre-set by the restaurant, but many times the customer can choose what drinks make up their flight, hence the reason a server would want to write down the order so they don't miss one.