Oranges are a citrus Citrus × ​sinensis (Citrus Sinensis (L.) Osbeck) and its fruit. It is the most commonly grown tree fruit in the world.

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

Trees of oranges are widely cultivated in tropical and subtropical climates for the delicious 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 State of Florida in the US.

Orange trees 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 "orange" name is thought to ultimately derive from the Sanskrit for the orange tree, with its final form developing after passing through numerous intermediate languages.

In a number of languages, the origange is known as a "Chinese apple" (e.g. Dutch Sinaasappel, "China's apple", or northern German Apfelsine). (In English, however, "Chinese apple" generally refers to the pomegranate.