A hamburger (or simply burger) is a sandwich that consists of a cooked patty of ground meat that is fried, steamed, grilled, or broiled, and is generally served with various condiments and toppings inside a sliced bun baked specially for this purpose. Hamburgers are often served with french fries or onion rings.
Hamburger also refers to the cooked patty of ground meat (usually beef) by itself. The patty alone is also known as a beefburger, or burger. This type of meat can be used in boxed dinners such as "Hamburger Helper". Hamburger is actually a distinct product from ground round and other types of ground meat. However, ground beef of any form is often commonly referred to as "hamburger." A recipe calling for 'hamburger' (the non-countable noun) would require ground beef or beef substitute- not a whole sandwich. Hamburger does not refer to ham.