(a) “Natural gas” means a mixture of hydrocarbons and small quantities of nonhydrocarbons existing in the gaseous phase.

(b) “Locomotive fuel” means diesel fuel and any other fuel except gasoline used as fuel in a railroad locomotive.

(c) “Person” means any individual, firm, copartnership, joint venture, association, corporation, estate, trust or any other combination acting as a unit, and the plural as well as the singular number unless the intention to give a more limited meaning is disclosed by the context.

(d) “Commission” or “department” means the Department of Revenue, acting either directly or through its duly authorized officers, agents or employees.

(e) “Permittee” means any person holding a user’s permit issued under the provisions of this article.

(f) “Industrial purposes” means the operation of machinery used for manufacturing.

(g) “Engine” or “motor” means internal combustion engine.

(h) “Manufacturer” means a person conducting an activity of an industrial or commercial nature wherein labor or skill is applied by hand or by machinery, to materials belonging to the manufacturer so that a new, different or more useful article of tangible personal property or article of trade or commerce is produced for sale or rental.

(i) “Custom processor” means a person who performs the services of a manufacturer upon the property of a customer.

(j) “Compressed gas” means gases derived from petroleum or natural gas which are in the gaseous state at normal atmospheric temperature and pressure, but which may be maintained in the liquid state at normal atmospheric temperature by suitable pressure. As used herein, the term shall be deemed to mean and include methane, ethane, propane, ethylene, propylene, butylene, butane, isobutane, and any and all liquid flammable materials derived from petroleum or natural gas having a vapor pressure exceeding forty (40) pounds per square inch, absolute, at one hundred (100) degrees Fahrenheit. Normal storage of these gases is a liquid under pressure.