High Quality Content by WIKIPEDIA articles! An invoice or bill is a commercial document issued by a seller to the buyer, indicating the products, quantities, and agreed prices for products or services the seller has provided the buyer. An invoice indicates the sale transaction only. Payment terms are independent of the invoice and are negotiated by the buyer and the seller. Payment terms are usually included on the invoice. The buyer could have already paid for the products or services listed on the invoice. Buyer can also have a maximum number of days in which to pay for these goods and is sometimes offered a discount if paid before the due date.