As used in this article: “Claimant agency” means any administrative unit of state, county, city or town government, including department, institution, commission, authority, or the office of Executive Secretary of the Supreme Court, any circuit or district court and the Internal Revenue Service. All state agencies and institutions shall participate in the setoff program. “Debtor” means any individual having a delinquent debt or account with any claimant agency which obligation has not been satisfied by court order, set aside by court order, or discharged in bankruptcy. “Delinquent debt” means any liquidated sum due and owing any claimant agency, or any restitution ordered paid to a clerk of the court pursuant to Title 19.2, including any amount of court costs or fines which have accrued through contract, subrogation, tort, operation of law, or any other legal theory regardless of whether there is an outstanding judgment for that sum which is legally collectible and for which a collection effort has been or is being made. “Mailing date of notice” means the date of notice appearing thereon. “Refund” means any individual’s (i) Virginia state or local income tax refund payable pursuant to § 58.1-309 or (ii) federal income tax refund payable pursuant to § 6402 of the Internal Revenue Code. This term also includes any refund belonging to a debtor resulting from the filing of a joint income tax return or a refund belonging to a debtor resulting from the filing of a return where married individuals have elected to file a combined return and separately state their Virginia taxable incomes under the provisions of subdivision B 2 of § 58.1-324.