The Krystal is a small sized burger topped with onions, mustard and dill pickle on a square, steamy bun.
More details on the Krystal website: http://krystal.com
About Krystal (from Wikipedia)
Krystal is an American fast food restaurant chain known for their small, square hamburger sliders with steamed-in onions and 24/7 business hours. Krystal is often described as the Southern equivalent of the Midwest American hamburger chain White Castle. Krystal has 420 locations.