The term "grass diet" typically refers to a type of feed or food for animals that consists primarily of grasses. This can include pasture, hay, silage, or other forms of dried grass. The phrase is often used in reference to grazing animals such as cows, sheep, and horses, who are fed on grasses grown specifically for them or collected from natural habitats. In some cases, the term may also be used more broadly to refer to a diet that includes significant amounts of plant-based foods, but this is not its primary meaning.