Unless specifically defined in the TCAA or in the rules of the commission, the terms used in this subchapter have the meanings commonly ascribed to them in the field of air pollution control. In addition to the terms which are defined by the TCAA, §§3.2, 101.1, and 114.1 of this title (relating to Definitions), the following words and terms, when used in this division shall have the following meanings, unless the context clearly indicates otherwise.(1) Incremental costs--The cost difference between the manufacturer's suggested retail price (MSRP) to purchase or lease a new on-road diesel vehicle certified by the EPA to meet the federal emission standards required at the date of its manufacture and the MSRP to purchase or lease a comparable new on-road diesel vehicle certified by the EPA to meet an emission standard at least as stringent as those specified in §114.609 of this title (relating to On-Road Diesel Vehicle Purchase or Lease Incentive Schedule).(2) Lease--The use and control of a new on-road diesel vehicle in accordance with a rental contract for a term of twelve consecutive months or more.(3) Lessee--A person who enters into a lease for a new on-road diesel vehicle.(4) Motor vehicle--A self-propelled device designed for transporting persons or property on a public highway that is required to be registered under Texas Transportation Code, Chapter 502.(5) New on-road diesel vehicle--An on-road diesel that has never been the subject of a first sale as defined under