Section 390(2)(e) in The Calcutta Municipal Corporation Act, 1980
(e)business buildings, that is to say, any buildings or part thereof used for transaction of business for the keeping of accounts and records or for similar purposes; such buildings shall include offices, banks, professional establishments, court house, and libraries for the principal function of transaction of public business and keeping of books and records, and shall also include office buildings (premises) solely or principally used as an office or for office purpose.