In this Act, unless the context otherwise requires,-

(26). "output tax", in relation to any period, means the aggregate amount of tax payable by a dealer liable to pay tax under section 10, section 11, section 12, section 14, sub-section (3) of section 24, and section 27C, and includes tax payable at the compounded rate under sub-section (3) of section 16 or sub-section (3A), or sub-section (3B), of section 16 or sub-section (4) of section 18, in respect of any sale, or purchase, of goods, or execution of works contract, made by him in West Bengal;