St. Louis-style barbecue refers to spare ribs associated with the St. Louis area. These are usually grilled rather than slow-cooked over indirect heat with smoke which is typically associated with the term "barbecue" in the United States.
Did you know that the sparerib comes from the belly area and are typically fatter with more meat on them. They are cut down into a rectangular shape, have flatter bones and when the cartilage and breastbone is trimmed away they are known as a St. Louis Style Sparerib.