White Castle’s small square hamburger is called a slider.
White Castle was founded in Wichita, Kansas, in 1921 by Walter Anderson and Billy Ingram. Its small, steam-grilled hamburgers became strongly associated with the chain and helped establish the fast-food restaurant model in the United States.
The term “slider” is now used more broadly for small sandwiches, but White Castle helped popularize it as a hamburger name. White Castle sliders are characteristically small, square patties cooked with onions and served in soft buns.
A common mix-up is confusing a slider with a specific White Castle menu item. “Slider” describes the sandwich style, while individual versions may include different toppings or fillings.