The leek, Allium ampeloprasum var. porrum (L.), also sometimes known as Allium porrum, is a vegetable which belongs, along with the onion and garlic, to family Amaryllidaceae, subfamily Allioideae. Two related vegetables, the elephant garlic and kurrat, are also variant subspecies of Allium ampeloprasum, although different in their uses as food.

The edible part of the leek plant is a bundle of leaf sheaths which is sometimes called a stem or stalk.