Thai or THAI may refer to:
- Of or from Thailand, a country in Southeast Asia.
- Thai people, Siamese people, Central/Southern Thai people or Thai noi people, an ethnic group from Central and Southern Thailand.
- Sukhothai language, a kind of Thai topolect, by the end of the 18th century, they gradually diverged into regional variants, which subsequently developed into the modern Central Thai and Southern Thai.
- Central Thai language or Siamese language, the sole official language in Thailand and first language of most people in Central Thailand, including Thai Chinese in Southern Thailand.
- Southern Thai language, or Southern Siamese language, or Tambralinga language, language of Southern Thailand first language of most people in Southern Thailand
- Thai script
- Thai (Unicode block)