A da'i (Arabic: داعي, dā‘ī) is someone who engages in da'wah, the act of inviting people to Islam.
In Dawoodi Bohra tradition
In the Fatimid era Ismaili faith, the term dā'ī has been used to refer to important religious leaders other than the hereditary Imams, and the Da'wa or "Mission" is a clerical-style organisation. Literally meaning "absolute missionary" or "unrestricted missionary", Da'i al-Mutlaq is nowadays the title of the head of the Dawoodi Bohra community.
References
Da'i Wikipedia(Text) CC BY-SA