<human>:  Why is a burger called a hamburger?
<bot>: The burger was first served in the US in the 1930s. It is named after the town of Hamburg, Germany. Hamburgers are made from beef, which is ground into a paste, and then formed into patties. The patties are cooked on a flat grill called a hamburger grill. Hamburgers are served on a bun, which is a type of bread. Hamburgers are usually served with ketchup and mustard.