Borneo (ˈbɔːrnioʊ; Kalimantan) is the third-largest island in the world, with an area of . At the geographic centre of Maritime Southeast Asia, it is one of the Greater Sunda Islands, located north of Java, west of Sulawesi, and east of Sumatra.
The island is politically divided among three countries: Malaysia and Brunei in the north, and Indonesia to the south. Approximately 73% of the island is Indonesian territory. In the north, the East Malaysian states of Sabah and Sarawak make up about 26% of the island. The population in Borneo is 23,053,723 (2020 national censuses). Additionally, the Malaysian federal territory of Labuan is situated on a small island just off the coast of Borneo. The sovereign state of Brunei, located on the north coast, comprises about 1% of Borneo's land area. A little more than half of the island is in the Northern Hemisphere, including Brunei and the Malaysian portion, while the Indonesian portion spans the Northern and Southern hemispheres.
The Native people of Borneo referred to their island as Pulu K'lemantang but not as an ethnic name, when the sixteenth century Portuguese explorer Jorge de Menezes made contact with the native which became the name for modern-day Indonesian Borneo. The term kelamantan is used in Sarawak to refer to a group of people who consume sago in the northern part of the island. According to Crowfurd, the word kelamantan is the name of a type of mango (Mangifera) so the island of Borneo is called a mango island by the native. But he adds that the word is fanciful and unpopular. The local mango, called klemantan, is still widely found in rural areas in Ketapang and surrounding areas of West Kalimantan.
Internationally it is known as Borneo, derived from European contact with the Brunei kingdom in the 16th century during the Age of Exploration. On a map from around 1601, Brunei city is referred to as Borneo, and the whole island is also labelled Borneo. The name Borneo may derive from the Sanskrit word váruṇa (वरुण), meaning either "water" or Varuna, the Hindu god of rain.