Section 38P. (a) As used in this section, the following terms shall have the following meanings:

''Break-bulk cargo'', shall mean general goods, commodities or wares which are customarily shipped in boxed, bagged, crated or unitized form, held in the vessel's general holding areas, and handled by the piece, unit or in separate lots; without limiting the generality of the foregoing definition of break-bulk cargo, that term shall include road motor vehicles and other odd-size cargo, but shall not include containerized cargo or bulk cargo.

''Bulk cargo'', shall mean unsegregated mass commodities including, without limitation, items such as petroleum products, coal and bulk salt which are carried loose and which are customarily loaded and unloaded by pumping, shoveling, scooping or other similar means.

''Containerized cargo'', shall mean general goods, commodities or wares that are shipped in non-disposable, reusable, commercial sized shipping containers that are customarily used on sea and ocean going vessels for the convenient shipment of such goods, commodities or wares.

(b) A corporation subject to the excise imposed under section thirty-nine shall be allowed a non-refundable credit for the qualifying harbor maintenance tax paid during the taxable year. Qualifying harbor maintenance tax shall be the tax paid to the federal government by a corporation as a shipper, importer or exporter pursuant to section forty-four hundred and sixty-one of the federal Internal Revenue Code subject to the following conditions and limitations: (1) the tax must be paid with respect to the shipment of break-bulk cargo or containerized cargo; (2) the tax must be paid with respect to shipment by sea and ocean-going vessels through ports located in this commonwealth; and (3) tax paid with respect to passengers, the shipment of bulk cargo or the shipment of any other cargo or item or commerce not included within the meaning of clause (1) hereof is not qualifying harbor maintenance tax.

(c) The credit allowed under this section for qualifying harbor maintenance tax shall not be subject to the limitations of section thirty-two C; provided, however, that the credit allowed by this section shall not reduce the excise due under this chapter below the minimum excise provided by section thirty-nine (b).

(d) Any unused credit may be carried forward from the year earned, and applied against the excise due from the taxpayer under this chapter in any of the succeeding five taxable years.