A fast food restaurant, also known as a Quick Service Restaurant or QSR within the industry itself, is a specific type of restaurant characterized both by its fast food cuisine and by minimal table service. Food served in fast food restaurants typically caters to a "meat-sweet diet" and is offered from a limited menu; is cooked in bulk in advance and kept hot; is finished and packaged to order; and is usually available ready to take away, though seating may be provided. Fast food restaurants are usually part of a restaurant chain or franchise operation, which provisions standardized ingredients and/or partially prepared foods and supplies to each restaurant through controlled supply channels. The term "fast food" was recognized in a dictionary by Merriam–Webster in 1951.

Arguably the first fast food restaurants originated in the United States with A&W in 1916 and White Castle in 1921. Today, American-founded fast food chains such as McDonald's and KFC are multinational corporations with outlets across the globe.

Fast food is the term given to food that can be prepared and served very quickly. While any meal with low preparation time can be considered to be fast food, typically the term refers to food sold in a restaurant or store with preheated or precooked ingredients, and served to the customer in a packaged form for take-out/take-away. The term "fast food" was recognized in a dictionary by Merriam–Webster in 1951.

Outlets may be stands or kiosks, which may provide no shelter or seating, or fast food restaurants (also known as quick service restaurants). Franchise operations which are part of restaurant chains have standardized foodstuffs shipped to each restaurant from central locations.

The concept of ready-cooked food for sale is closely connected with urban development. In Ancient Rome cities had street stands that sold bread, sausages and wine.

In the cities of Roman antiquity, much of the urban population living in insulae, multi-story apartment blocks, depended on food vendors for much of their meals. In the mornings, bread soaked in wine was eaten as a quick snack and cooked vegetables and stews later in the day at a popina, a simple type of eating establishment. In the Middle Ages, large towns and major urban areas such as London and Paris supported numerous vendors that sold dishes such as pies, pasties, flans, waffles, wafers, pancakes and cooked meats. As in Roman cities during antiquity, many of these establishments catered to those who did not have means to cook their own food, particularly single households. Unlike richer town dwellers, many often could not afford housing with kitchen facilities and thus relied on fast food. Travellers, as well, such as pilgrims en route to a holy site, were among the customers.