A dairy is a business enterprise established for the harvesting of animal milk—mostly from cows or goats, but also from buffalo, sheep, horses or camels —for human consumption. A dairy is typically located on a dedicated dairy farm or section of a multi-purpose farm that is concerned with the harvesting of milk.

Terminology differs between countries. For example, in the United States, a farm building where milk is harvested is often called a milking parlor. In New Zealand such a building is historically known as the milking shed - although in recent years there has been a progressive change to call such a building a farm dairy.

In some countries, especially those with small numbers of animals being milked, as well as harvesting the milk from an animal, the dairy may also process the milk into butter, cheese and yogurt, for example. This is a traditional method of producing specialist milk products, especially in Europe. In the United States a dairy can also be a place that processes, distributes and sells dairy products, or a room, building or establishment where milk is stored and processed into milk products, such as butter or cheese. In New Zealand English the singular use of the word dairy almost exclusively refers to the corner convenience store, or superette. This usage is historical as such stores were a common place for the public to buy milk products.

As an attributive, the word dairy refers to milk-based products, derivatives and processes, and the animals and workers involved in their production: for example dairy cattle, dairy goat. A dairy farm produces milk and a dairy factory processes it into a variety of dairy products. These establishments constitute the dairy industry, a component of the food industry.