Lansium domesticum, commonly known as langsat, lanzone, longkong, or duku, is a tropical fruit-bearing tree in the Meliaceae family (the mahogany family). It is native to the western regions of Southeast Asia, specifically the Malay Peninsula, Borneo, Sumatra, and Java. The genus name Lansium is derived from the Malay word langsat, while the species epithet domesticum indicates its long history of cultivation and association with human settlements. Historically, this tree has been a quintessential garden fruit across the humid tropics of Asia, valued for its shade as much as its succulent, cooling fruit. In many regions, distinct varieties—such as the larger, thicker-skinned duku and the smaller, thinner-skinned longkong—are recognized by their varying levels of sweetness and acidity.

The tree is a medium-sized evergreen that can grow up to 20 meters tall, featuring pinnate, dark green, leathery leaves and a straight trunk with smooth, greyish-brown bark. Its flowers are small, cream-colored, and produced in clusters directly on the trunk and older branches—a botanical characteristic known as cauliflory. The fruit itself is a translucent, juicy berry with a leathery, pale yellow, and often velvety skin. Inside, it is divided into five or six segments containing white, translucent arils. Some of these segments hold flat, bitter green seeds, while others may be seedless. Lansium domesticum thrives in hot, humid, low-elevation tropical environments with fertile, well-drained soil, and it is highly susceptible to cold, making it a true tropical specialist.

The fruit of Lansium domesticum is cherished for its refreshing, "sweet-tart" flavor profile, often described as a sophisticated cross between a grapefruit and a grape, with a hint of floral perfume. It is almost exclusively consumed fresh as a table fruit; the arils are prized for their melting texture and ability to quench thirst in hot weather. In some Southeast Asian culinary traditions, the slightly bitter seeds are sometimes processed into traditional medicines or dried to be used in tinctures. Because the skin exudes a sticky latex, the fruit is often handled with care during harvest to ensure it does not become too tacky, though this latex is easily avoided once the fruit is peeled.

Nutritionally, the fruit is a good source of dietary fiber, Vitamin C, Vitamin B1 (thiamine), and riboflavin. Its biochemical profile is notable for the presence of triterpenoids—specifically onoceranoid types—which are responsible for the distinct, slightly bitter quality of the seeds and the skin. The peel and seeds are particularly rich in bioactive compounds, including limonoids, which have been the focus of modern scientific study for their potential antioxidant and anti-inflammatory properties. In traditional folk medicine, the dried rind of the fruit is often burned as an aromatic incense to ward off mosquitoes and soothe respiratory discomfort, while the bark is occasionally prepared as a decoction to treat dysentery.