An orange—specifically, the sweet orange—is the citrus Citrus × ​sinensis (Citrus sinensis (L.) Osbeck) and its fruit. It is the most commonly grown tree fruit in the world.

The orange is a hybrid of ancient cultivated origin, possibly between pomelo (Citrus maxima) and mandarin (Citrus reticulata). It is an evergreen flowering tree generally growing to 9–10 m in height (although very old specimens have reached 15 m). The leaves are arranged alternately, are ovate in shape with crenulate margins and are 4–10 cm long. The orange fruit is a hesperidium, a type of berry.

Orange trees are widely cultivated in tropical and subtropical climates for the sweet fruit, which is peeled or cut (to avoid the bitter rind) and eaten whole, or processed to extract orange juice, and also for the fragrant peel. In 2008, 68.5 million tons of oranges were grown worldwide, primarily in Brazil and the US states California and Florida.

Oranges probably originated in Southeast Asia and were cultivated in China by 2500 BC. The fruit of Citrus sinensis is called sweet orange to distinguish it from Citrus aurantium, the bitter orange. The name is thought to derive ultimately from the Sanskrit for the orange tree, with its final form developing after passing through numerous intermediate languages.