The Kra-Dai language family, also known as Tai-Kadai, is a group of languages primarily spoken in Southeast Asia and southern China. It includes languages such as Thai, Lao, and Zhuang. The family is known for its tonal languages, where the meaning of a word can change based on pitch. Linguists believe that the Kra-Dai languages originated in southern China and gradually spread to other regions. The family is characterized by its unique phonetic and grammatical features, which distinguish it from other language families in the area, such as Sino-Tibetan and Austroasiatic.