The djong, jong, or jung is a type of sailing ship originating from Java, Indonesia that was widely used by Javanese, Sundanese, and later, by Malay sailors. The word was and is spelled jong in its languages of origin, the "djong" spelling being the colonial Dutch romanization. In English, the djong lends its name to other ships of similar configuration, called junks, and to their characteristic style of rigging, the junk rig.
Djongs are used mainly as seagoing passenger and cargo vessels. They traveled as far as the Atlantic Ocean in the medieval era. Their tonnage ranged from 40 to 2000 deadweight tons, with an average deadweight of 1200–1400 tons during the Majapahit era. Javanese kingdoms such as Majapahit, Demak Sultanate, and Kalinyamat Sultanate used these vessels as warships, but still predominantly as transport vessels. Mataram Sultanate primarily used jong as a merchant ship rather than a warship.
For their war fleet, the Malays prefer to use shallow draught, oared longships similar to the galley, such as lancaran, penjajap, and kelulus. This is very different from the Javanese who prefer long-range, deep-draught round ships such as jong and malangbang. The reason for this difference is that the Malays operated their ships in riverine water, sheltered straits zone, and archipelagic environment, while the Javanese are often active in the open and high sea. After contact with Iberian people, both the Javanese and Malay fleets began to use the ghurab and ghali more frequently.
Views diverge on whether the origin of the word is from a dialect of Chinese, or a Javanese word. The word jong, jung, or junk may derive from the Chinese word chuán (, "boat; ship"). However, Paul Pelliot and Waruno Mahdi reject the Chinese origin of the name. Instead, it may be derived from "jong" (transliterated as joṅ) in Old Javanese which means ship. The first record of Old Javanese jong comes from an inscription in Bali dating to the 11th century CE.