Kalimantan is the Indonesian name for the island known to the rest of the world as "Borneo". Thus, for outsider the meaning of "Kalimantan" is simply the Indonesian part of the island of Borneo, which occupies the central and southern regions of the island. The Indonesian Kalimantan is bordered to the north by the Malaysian states of Sarawak and Sabah. "Borneo" is a word created by the westerners from "Brunei", while the natives have always call the island "Kalimantan". In his correspondence with the Dutch residency in 1857, Prince Tamjidillah of Banjar Kingdom mentioned about Kalimantan island and not Borneo island. This shows that for the locals the name Kalimantan is more popular than Borneo, the name used by the Dutch in their administrative.

There are some theories about the origin of the word "Kalimantan". The first one, "Borneo" is a word derived from "Brunei" of the Sultanate of Brunei Darussalam which was a big kingdom back then, with its territories including Sarawak and a part of Sabah (because some part belonged to the sulatanate of Sulu-Mindanao). The Portuguese merchants called the island "Borneo" and the name is popular among Europeans. But the natives call the island with "Pulo Klemantan" (Klemantan Island). The second theory, according to Crowfurd in the Descriptive Dictionary of the Indian Island (1856), the word "Kalimantan" is a kind of mango which made Kalimantan as an island of mangoes but he added that that word has inclination toward fairy tale and was not popular.

The indigenous populations of Kalimantan are divided into Dayaks, Malays (particularly in West Kalimantan and along coastal lines), and Banjarese-Malay (in South Kalimantan). There are also many migrants from other parts of the region such as Buginese, Javanese, Madurese, and Chinese who are concentrated in West Kalimantan. There was a war in the region between the indigenous Dayaks and Madurese immigrants, who were moved here as part of a government transmigration program that operated, in various forms, from 1905 until 2001. The Dayak fighters are known for their ferocious tactics, such as the beheading and mutilation of their victims. In the past, Dayaks who converted to Islam were considered Malay or Banjar. They then moved from their ancestral homeland into the country, mainly near rivers. One of the groups is called "Senganan", and they live along the Kapuas river in Sanggau, West Kalimantan. Recently, however, there is an increasing pride among Muslims of Dayak descendants to consider themselves Dayak again. The Dayaks whose religion is mainly Islam, and who retained their Dayak identity, are Bakumpai who can be found in South Kalimantan and along the Mahakam River, East Kalimantan, as well as Lamandau in Central Kalimantan. East Kalimantan, as well as Lamandau in Central Kalimantan.