72 Pa. Stat. § 3310-103
The following words and phrases when used in this act shall have the meanings given to them in this section unless the context clearly indicates otherwise:
"Assessment." An assessment, determination, settlement or appraisement of tax liability issued by the Department of Revenue.
"Department." The Department of Revenue of the Commonwealth.
"Fiscal Code." The act of April 9, 1929 (P.L. 343, No. 176), known as The Fiscal Code.
"Secretary." The Secretary of Revenue of the Commonwealth.
"Taxpayer." An individual, partnership, association, society, company, corporation, estate, trust, trustee, receiver, liquidator, fiduciary or other entity subject to or claiming exemption from any tax administered by the Department of Revenue pursuant to the authority of the laws of this Commonwealth or under a duty to perform an act for itself or for another under or pursuant to the authority of such laws.
"Voluntary payment." A payment of a tax liability made pursuant to the free will of the taxpayer. The term does not include a payment made as a result of distraint, levy or pursuant to a legal proceeding in which the Commonwealth is seeking to collect its delinquent taxes or file a claim therefor.
72 P.S. § 3310-103