Hadza is a language of Tanzania. It has only about 200 speakers. Hadza is classified as a Khoisan language by Greenberg (1976), along with Sandawe, its neighbouring language. The reasons for this classification include the presence of clicks in the language and a relatively small number of proposed cognates with the better-known Khoisan languages. Because of its seemingly typological nature, this classification is disputed, but relatively little research has been undertaken as to what the genetic affiliation of Hadza and Sandawe might be.
Sands, Bonny E. (1998) 'The Linguistic Relationship between Hadza and Khoisan' In Schladt, Matthias (ed.) Language, Identity, and Conceptualization among the Khoisan (Quellen zur Khoisan-Forschung Vol. 15), Köln: Rüdiger Köppe, 265-283.
A language family is a group of genetically related languages said to have descended from a common proto-language.
Language families can be divided into smaller phylogenetic units, conventionally referred to as branches of the family, because the history of a language family is often represented as a tree diagram.
Languages that cannot be reliably classified into any family are known as language isolates.