An invoice, bill or tab is a commercial document issued by a seller to a buyer, relating to a sale transaction and indicating the products, quantities, and agreed prices for products or services the seller had provided the buyer.Payment terms are usually stated on the invoice. These may specify that the buyer has a maximum number of days in which to pay, and is sometimes offered a discount if paid before the due date. The buyer could have already paid for the products or services listed on the invoice.In the rental industry, an invoice must include a specific reference to the duration of the time being billed, so in addition to quantity, price and discount the invoicing amount is also based on duration. Generally each line of a rental invoice will refer to the actual hours, days, weeks, months, etc., being billed.From the point of view of a seller, an invoice is a sales invoice. From the point of view of a buyer, an invoice is a purchase invoice. The document indicates the buyer and seller, but the term invoice indicates money is owed or owing.