What does "short order" mean?

Quickly; see in short order.

An order of food to be prepared and served quickly, as in It's just a diner, serving short orders exclusively. This expression, dating from about 1890, gave rise to the adjective short-order, used not only in short-order cook, a cook specializing in short orders, but in other terms such as short-order divorce, a divorce quickly obtained owing to liberal divorce laws.