Collard is a group of loose-leafed cultivars of Brassica oleracea (the same species as many common vegetables like cabbage and broccoli). Part of the acephala cultivar group (or kale group), collard is also classified as the variety B. oleracea var. viridis.

The plants are grown as a food crop for their large, dark-green, edible leaves, which are cooked and eaten as vegetables. Collard greens have been cultivated as food since classical antiquity.

The term colewort is a medieval term for non-heading brassica crops.

The term collard has been used to include many non-heading Brassica oleracea crops. While American collards are best placed in the Viridis crop group, the acephala (Greek for 'without a head') cultivar group is also used referring to a lack of close-knit core of leaves (a "head") like cabbage does, making collards more tolerant of high humidity levels and less susceptible to fungal diseases.

In Africa, it is known as sukuma (East Africa), muriwo or umBhida. In Kashmir, it is known as haakh (Kashmir).

The plant is a biennial where winter frost occurs; some varieties may be perennial in warmer regions. It has an upright stalk, often growing over two feet tall and up to six feet for the Portuguese cultivars. Popular cultivars of collard greens include 'Georgia Southern', 'Vates', 'Morris Heading', 'Blue Max', 'Top Bunch', 'Butter Collard' (couve manteiga), couve tronchuda, and Groninger Blauw.

Collard is generally described as part of the Acephala (kale) cultivar group, but is also classified as the variety B. oleracea var. viridis.

The plant is commercially cultivated for its thick, slightly bitter, edible leaves. They are available year-round, but are tastier and more nutritious in the cold months, after the first frost.^{[citation needed]} For best texture, the leaves are picked before they reach their maximum size, at which stage they are thicker and are cooked differently from the new leaves. Age does not affect flavor.^{[citation needed]}