1 Huffman: As long as I live, I'll never forget the look on that alien's face... 2  squeal, Crypto 136, squeal like a pig! 3  And he did, dammit! [he is vaporized]. 4  Mayor: Now that you are all here, I'd like to say, err... 5  please stay in your homes.
What is an 'Invoice'. An invoice is a commercial document that itemizes a transaction between a buyer and a seller. If goods or services were purchased on credit, the invoice usually specifies the terms of the deal, and provide information on the available methods of payment. An invoice is also known as a bill or sales invoice.
Invoice is what one would bill for payment with. Voucher is an internal document or documents the Government uses as the evidence to pay a bill. You might try looking in your agencies finance regualtions, policies, handbooks etc. as I suspect 'voucher will be defined there somewhere.