A credit memo or credit memorandum is a document issued by the seller of goods or services to the buyer, reducing the amount that the buyer owes to the seller under the terms of an earlier invoice. One type of credit memo is issued by a seller in order to reduce the amount that a customer owes from a previously issued sales invoice. The credit memo usually includes details of exactly why the amount stated on the memo has been issued, which can be used later to aggregate information about credit memos to determine why the seller is issuing them.