http://en.wikipedia.org/wiki/Types_of_restaurants

Historically, restaurant referred only to places which provide tables where one sits down to eat the meal, typically served by wait-staff. Following the rise of fast food and take-out restaurants, a retronym for the older "standard" restaurant was created, sit-down restaurant. Most commonly, "sit-down restaurant" refers to a casual dining restaurant with table service rather than a fast-food restaurant where one orders food at a counter. Sit-down restaurants are often further categorized as "family-style" or "formal".

In British English, the term "restaurant" almost always means an eating establishment with table service, so the "sit-down" qualification is not usually necessary. Fast food and takeaway (takeout) outlets with counter service are not normally referred to as restaurants.