Dai can mean:
- Dai people, one of the 56 recognized ethnic minorities of China
- Dai (Yindu), ethnic tribe of Chin, Myanmar
- Dai County, in Shanxi, China
- Dai (Spring and Autumn Period), a state during the Spring and Autumn Period
- Dai (Sixteen Kingdoms), a Xianbei state during the Sixteen Kingdoms era of history of China
- Dai (Warring States period), a short-lived state during the Warring States period.
- Da'i (Arabic: "missionary") refers to a person who engages in Dawah, the act of inviting people to Islam
- A greeting and farewell used by the wizards in Diane Duane's Young Wizards series