The durian is the fruit of several tree species belonging to the genus Durio and the Malvaceae family (although some taxonomists place Durio in a distinct family, Durionaceae). Widely known and revered in southeast Asia as the "king of fruits", the durian is distinctive for its large size, unique odour, and formidable thorn-covered husk. The fruit can grow as large as 30 centimetres (12 in) long and 15 centimetres (6 in) in diameter, and it typically weighs one to three kilograms (2 to 7 lb). Its shape ranges from oblong to round, the colour of its husk green to brown, and its flesh pale yellow to red, depending on the species.

The edible flesh emits a distinctive odour, strong and penetrating even when the husk is intact. Some people regard the durian as fragrant; others find the aroma overpowering and offensive. The smell evokes reactions from deep appreciation to intense disgust. The odour has led to the fruit's banishment from certain hotels and public transportation in southeast Asia.

The durian, native to Brunei, Indonesia and Malaysia, has been known to the Western world for about 600 years. The 19th-century British naturalist Alfred Russel Wallace famously described its flesh as "a rich custard highly flavoured with almonds". The flesh can be consumed at various stages of ripeness, and is used to flavour a wide variety of savoury and sweet edibles in Southeast Asian cuisines. The seeds can also be eaten when cooked.

There are 30 recognised Durio species, at least nine of which produce edible fruit. Durio zibethinus is the only species available in the international market: other species are sold in their local regions. There are hundreds of durian cultivars; many consumers express preferences for specific cultivars, which fetch higher prices in the market.

Durian trees are large, growing to 25–50 metres (80–165 ft) in height depending on the species. The leaves are evergreen, elliptic to oblong and 10–18 centimetres (4–7 in) long. The flowers are produced in three to thirty clusters together on large branches and directly on the trunk with each flower having a calyx (sepals) and five (rarely four or six) petals. Durian trees have one or two flowering and fruiting periods per year, though the timing varies depending on the species, cultivars, and localities. A typical durian tree can bear fruit after four or five years. The durian fruit can hang from any branch and matures roughly three months after pollination. The fruit can grow up to 30 centimetres (12 in) long and 15 centimetres (6 in) in diameter, and typically weighs one to three kilograms (2 to 7 lb). Its shape ranges from oblong to round, the colour of its husk green to brown, and its flesh pale-yellow to red, depending on the species. Among the thirty known species of Durio, nine of them have been identified as producing edible fruits: D. zibethinus, D. dulcis, D. grandiflorus, D. graveolens, D. kutejensis, D. lowianus, D. macrantha, D. oxleyanus and D. testudinarum. However, there are many species for which the fruit has never been collected or properly examined, so other species with edible fruit may exist. The durian is also somewhat similar in appearance to the jackfruit, an unrelated species.

The name durian comes from the Malay word duri (thorn) together with the suffix -an (for building a noun in Malay).  D. zibethinus is the only species commercially cultivated on a large scale and available outside of its native region. Since this species is open-pollinated, it shows considerable diversity in fruit colour and odour, size of flesh and seed, and tree phenology. In the species name, zibethinus refers to the Indian civet, Viverra zibetha. There is disagreement regarding whether this name, bestowed by Linnaeus, refers to civets being so fond of the durian that the fruit was used as bait to entrap them, or to the durian smelling like the civet.

Durian flowers are large and feathery with copious nectar, and give off a heavy, sour and buttery odour. These features are typical of flowers pollinated by certain species of bats that eat nectar and pollen. According to research conducted in Malaysia in the 1970s, durians were pollinated almost exclusively by cave fruit bats (Eonycteris spelaea). However, a 1996 study indicated two species, D. grandiflorus and D. oblongus, were pollinated by spiderhunters (Nectariniidae) and another species, D. kutejensis, was pollinated by giant honey bees and birds as well as bats.