What does an invoice represent?

An invoice serves as a formal record of a sale to a customer. It details the products or services rendered, the total amount due, payment terms, and any applicable taxes. This document is crucial in financial transactions as it not only signifies that a transaction has taken place but also outlines the customer's obligation to pay for those goods or services.

While the other options touch on related concepts in the sales and billing process, they do not fully capture the primary purpose of an invoice. For example, a notification of shipment indicates that goods are on their way but does not necessarily reflect a completed sale until an invoice is issued. A payment reminder serves the purpose of prompting customers to pay but is not a record of the transaction itself. An estimate of service charges is a preliminary document provided before a sale to convey potential costs, but it does not fulfill the role of documenting an actual completed transaction like an invoice does.