Rapeseed (Brassica napus subsp. napus), also known as rape and oilseed rape and canola, is a bright-yellow flowering member of the family Brassicaceae (mustard or cabbage family), cultivated mainly for its oil-rich seed, which naturally contains appreciable amounts of mildly toxic erucic acid. The term "canola" denotes a group of rapeseed cultivars that were bred to have very low levels of erucic acid and which are especially prized for use as human and animal food. Rapeseed is the third-largest source of vegetable oil and the second-largest source of protein meal in the world.

Brassica napus grows to 100 centimetres (39 inches) in height with hairless, fleshy, pinnatifid and glaucous lower leaves which are stalked whereas the upper leaves have no petioles.

Rapeseed flowers are bright yellow and about 17 millimetres (3⁄4 in) across. They are radial and consist of four petals in a typical cross-form, alternating with four sepals. They have indeterminate racemose flowering starting at the lowest bud and growing upward in the following days. The flowers have two lateral stamens with short filaments, and four median stamens with longer filaments whose anthers split away from the flower's center upon flowering.

The rapeseed pods are green and elongated siliquae during development that eventually ripen to brown. They grow on pedicels 1 to 3 cm (3⁄8 to 1+3⁄16 in) long, and can range from 5 to 10 cm (2 to 4 in) in length. Each pod has two compartments separated by an inner central wall within which a row of seeds develops. The seeds are round and have a diameter of 1.5 to 3 mm (1⁄16 to 1⁄8 in). They have a reticulate surface texture, and are black and hard at maturity.

B. napus can be distinguished from B. nigra by the upper leaves which do not clasp the stem, and from B. rapa by its smaller petals which are less than 13 mm (1⁄2 in) across.

The species Brassica napus belongs to the flowering plant family Brassicaceae. Rapeseed is a subspecies with the autonym B. napus subsp. napus. It encompasses winter and spring oilseed, vegetable and fodder rape. Siberian kale is a distinct leaf rape form variety (B. napus var. pabularia) which used to be common as a winter-annual vegetable. The second subspecies of B. napus is B. napus subsp. rapifera (also subsp. napobrassica; the rutabaga, swede, or yellow turnip).

B. napus is a digenomic amphidiploid that occurred due to the interspecific hybridization between B. oleracea and B. rapa. It is a self-compatible pollinating species like the other amphidiploid Brassica species.

The term "rape" derives from the Latin word for turnip, rāpa or rāpum, cognate with the Greek word ῥάφη, rhaphe.