An orange—specifically, the sweet orange—is the citrus Citrus × sinensis (Citrus sinensis (L.) Osbeck) and its fruit. It was the most commonly grown tree fruit in the world (as of 1987).
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 high (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. (Source: Wikipedia)