The river has a total drainage area exceeding 1,165,000 km2 (450,000 sq mi). Its estimated annual flow stands at around 243 km3 (58 cu mi), twice that of the Nile River and three times that of the Tigris and Euphrates rivers combined, making it the twenty-first largest river in the world in terms of annual flow. The Zanskar is its left bank tributary in Ladakh. In the plains, its left bank tributary is the Panjnad which itself has five major tributaries, namely, the Chenab, Jhelum, the Ravi, the Beas, and the Sutlej. Its principal right bank tributaries are the Shyok, the Gilgit, the Kabul, the Gomal, and the Kurram. Beginning in a mountain spring and fed with glaciers and rivers in the Himalayas, the river supports ecosystems of temperate forests, plains and arid countryside.
The northern part of the Indus Valley, with its tributaries, forms the Punjab region, while the lower course of the Indus is known as Sindh and ends in a large delta. The river has historically been important to many cultures of the region. The 3rd millennium BC saw the rise of a major urban civilization of the Bronze Age. During the 2nd millennium BC, the Punjab region was mentioned in the hymns of the Hindu Rigveda as Sapta Sindhu and the Zoroastrian Avesta as Hapta Hindu (both terms meaning "seven rivers"). Early historical kingdoms that arose in the Indus Valley include Gandhāra, and the Ror dynasty of Sauvīra. The Indus River came into the knowledge of the West early in the Classical Period, when King Darius of Persia sent his Greek subject Scylax of Caryanda to explore the river, ca. 515 BC.
This river was known to the ancient Indians in Sanskrit as Sindhu, which is literally interpreted to mean "large body of water, sea, or ocean". The Proto-Iranian sound change *s > h occurred between 850–600 BCE, according to Asko Parpola, causing its Avestan name to become Hendu, From Iran, the name passed to the Greeks as Indós ("Ἰνδός") and to the Romans as Indus. The Persian name for the river was Darya, which similarly has the connotations of large body of water and sea.
However, linguists state that the original meaning of Sindhu/Hindu was not a body of water, but rather a frontier or bank. The Indus river formed the frontier between the Iranian peoples and Indo-Aryan peoples.