Casual Taxable Person has been defined in Section 2 (20) of the CGST Act. It means a person who occasionally undertakes transactions involving supply of goods or services or both in the course or furtherance of business, whether as principal, agent or in any other capacity, in a State or a Union territory where he has no fixed place of business.
(ICAI FAQ PUBLICATIONS 06-09-2017 REGISTRATION: FAQ NO. 19)