Section 18-501 - Definitions(a) In this subtitle the following words have the meanings indicated.(b) "Payment date" means the date of the Commission's check.(c) "Proper invoice" means an invoice that: (1) contains: (i) the contractor's federal employer identification number or Social Security number; and(ii) the contract or purchase order number or other description of the contract; and(2) contains or is accompanied by substantiating information and documentation as required by regulation or contract.(d) "Receipt date" means the date that a proper invoice is received by the Commission.