The Dayak ('daI.@k; older spelling: Dajak) or Dyak or Dayuh are one of the native groups of Borneo. It is a loose term for over 200 riverine and hill-dwelling ethnic groups, located principally in the central and southern interior of Borneo, each with its own dialect, customs, laws, territory, and culture, although common distinguishing traits are readily identifiable. Dayak languages are categorised as part of the Austronesian languages. The Dayak were animist (Kaharingan and Folk Hindus) in belief; however, since the 19th century there has been mass conversion to Christianity as well as Islam due to the spreading of Abrahamic religions.
It is commonly assumed that the name originates from the Bruneian and Melanau word for “interior people”, without any reference to an exact ethnic group. The term was adopted by Dutch and German authors as an umbrella term for any non-Muslim natives of Borneo. Thus, historically, the difference between Dayaks and non-Dayaks natives could be understood as a religious distinction. English writers disapproved the classification made by the Dutch and Germans, with James Brooke preferring to use the term Dayak for only two distinct groups, the Land (Bidayuh) and Sea Dayaks (Iban).
The Dutch classification from the 19th century has since continued in Indonesia as a catch-all term for indigenous, often non-Muslim tribes on the island until today. The term gained traction in the early 1900s among rising middle class and intellectual figures (such as Hausman Baboe) from those tribes and being used as a unifying term for Dayaks in Kalimantan. In Malaysia, the term Dayak generally reserves as an almost exclusively reference to the Iban (previously referred as Sea Dayaks) and Bidayuh (known as Land Dayak in the past).
Dayaks do not speak just one language. Their indigenous languages belong to different subgroups of the Malayo-Polynesian languages, such as Land Dayak, Malayic, Sabahan, and Barito languages. Nowadays most Dayaks are bilingual, in addition to their native language, are well-versed in Indonesian and Malay, depending on their country of origin.