As used in KRS 81A.532 to 81A.536, unless the context requires otherwise:
(1) "Commercial purposes" means the use of land, buildings, or structures, or parts thereof, for the buying, selling, storage, or shipment of goods or services, or other substantially similar types of activity;
(2) "District" means a designated county industrial district;
(3) "Industrial purposes" means the use of land, buildings, or structures, or parts thereof, for manufacturing, production or assembly of goods, warehousing and distribution, or other substantially similar types of activity; and (4) "Substantial investment" means expenditures by the county in an amount equal to or greater than twenty percent (20%) of the total assessed value of real property at the time of the designation of a designated county industrial district in utility, transportation, or other similar infrastructure within the district, not including normal or routine county road maintenance.