"Junk food" is a term used to describe food that is high in calories from sugar and/or fat, and possibly sodium, but with little dietary fiber, protein, vitamins, minerals, or other important forms of nutritional value. It is also known as HFSS food (high in fat, salt and sugar). The term junk food is a pejorative dating back to the 1950s.

Precise definitions vary by purpose and over time. Some high-protein foods, like meat prepared with saturated fat, may be considered junk food. Fast food and fast food restaurants are often equated with junk food, although fast foods cannot be categorically described as junk food. Most junk food is highly processed food.

Concerns about the negative health effects resulting from a junk food-heavy diet, especially obesity, have resulted in public health awareness campaigns, and restrictions on advertising and sale in several countries. Current studies indicate that a diet high in junk food can increase the risk of depression, digestive issues, heart disease and stroke, type 2 diabetes, cancer, and early death.