The crossword solution for the term 'Hamburger Order' is 'PLAIN, ' which is a five-letter word. A PLAIN hamburger is a classic American fast food dish consisting of a patty of ground beef, usually served on a bun with condiments such as ketchup, mustard, mayonnaise, lettuce, tomato, pickles, and onions. It is one of the most popular types of hamburgers and is often served with fries or other side dishes.