Welcome to PF, WhiteTim.
Short-order generally implies a high turn-over for rush crowds. Think of a diner at lunch-time. It's fast food, but usually of a higher quality and complexity than something like McDonalds.
edit: Hey, Cyrus. You beat me to it again.
and heart attacks.All good answers, WT. If you live near a Waffle House, sit at the counter and order breakfast. You'll see what a good short-order cook can pull off. They are always on the move, and the thing that saves them from burn-out is the limitations of their menus. They can cook for a whole restaurant-full of breakfast fans. Home-fried potatoes, fried or scrambled eggs, corned beef hash, bacon, sausage, biscuits, pancakes... If you only cook simple but tasty foods you can put out an impressive volume of food from a single kitchen. Give those guys enough griddle-space and simple utensils, and watch the magic.