The cashew (Anacardium occidentale; syn. Anacardium curatellifolium A.St.-Hil.) is a tree in the flowering plant family Anacardiaceae. The plant is native to northeastern Brazil. Its English name derives from the Portuguese name for the fruit of the cashew tree, caju, which in turn derives from the indigenous Tupi name, acajú. It is now widely grown in tropical climates for its cashew "nuts" (see below) and cashew apples.

It is a small evergreen tree growing to 10-12m (~32 ft) tall, with a short, often irregularly-shaped trunk. The leaves are spirally arranged, leathery textured, elliptic to obovate, 4 to 22 cm long and 2 to 15 cm broad, with a smooth margin. The flowers are produced in a panicle or corymb up to 26 cm long, each flower small, pale green at first then turning reddish, with five slender, acute petals 7 to 15 mm long.

What appears to be the fruit of the cashew tree is an oval or pear-shaped accessory fruit or false fruit that develops from the receptacle of the cashew flower. Called the cashew apple, better known in Central America as "marañón", it ripens into a yellow and/or red structure about 5–11 cm long. It is edible, and has a strong "sweet" smell and a sweet taste. The pulp of the cashew apple is very juicy, but the skin is fragile, making it unsuitable for transport. It is often used as a flavor in agua fresca.

The true fruit of the cashew tree is a kidney or boxing-glove shaped drupe that grows at the end of the pseudofruit. Actually, the drupe develops first on the tree, and then the peduncle expands into the pseudofruit. Within the true fruit is a single seed, the cashew nut. Although a nut in the culinary sense, in the botanical sense the fruit of the cashew is a seed. The seed is surrounded by a double shell containing a dermatogenic phenolic resin, urushiol, a potent skin irritant toxin also found in the related poison ivy. Some people are allergic to cashew nuts, but cashews are a less frequent allergen than nuts or peanuts.

Other names include: cajueiro, cashu, casho, acajuiba, caju, acajou, acaju, acajaiba, alcayoiba, anacarde, anacardier, anacardo, Andi parippu (in Malayalam), cacajuil, cajou, gajus, godambi (in Kannada), jeedi pappu (in Telugu), jocote maranon, maranon, merey, Mundhiri paruppu (Tamil), noix d'acajou, pomme cajou, pomme, jambu, jambu golok, jambu mete, jambu monyet, jambu terong, kasoy (Tagalog), and hạt điều in Vietnamese language. In the Antilles in Puerto Rico, it is known as pajuil, Indian nut in Slovenia, and in the Dominican Republic as the cajuil. The pseudofruit is the main part used as raw fruit.