Fast food is food prepared and served quickly at restaurants designed for speed and convenience. When you order at McDonald's, Burger King, or Taco Bell, you're buying fast food. These restaurants cook popular items like hamburgers, french fries, pizza, and chicken nuggets in advance or very rapidly, so customers can get their meals in minutes rather than waiting 30 or 40 minutes like at a traditional restaurant.

The term also describes the entire industry of these quick-service restaurants. Fast food became popular in America in the 1950s and 1960s as more families owned cars and wanted convenient meals. Restaurants like McDonald's pioneered systems where every burger was made the same way, every time, at thousands of locations. This standardization meant you knew exactly what you'd get whether you were in Maine or California.

Fast food restaurants typically have simple menus, lower prices than sit-down restaurants, and focus on efficiency: getting customers through quickly. Many have drive-through windows so people can order without leaving their cars. The food itself is usually high in calories, salt, and fat, which can make it taste good but less nutritious than home-cooked meals.

The phrase can also describe anything done too quickly without enough care: if you rush through your homework sloppily, someone might say you gave it the “fast food treatment.”