Definition of an Invoice
An invoice received from a supplier shows the items purchased, the cost per unit, the total cost or extension of each item, the total of all the items listed on the invoice, the terms of the sale, etc.
Definition of a Statement
A statement from a supplier lists the amounts from past invoices that the customer has not paid. For example, the statement from a supplier might indicate that as of July 31 the customer owes the entire amounts from four invoices and a small amount from a fifth invoice.
However, it is possible that the statement amount is not the current amount owed. For instance, it is possible that on July 30 and on August 3 the customer had paid the amounts owed for two of the invoices listed on the statement. For this reason, companies are wise to have the policy to make payments only from invoices and never from statements. The purpose of this policy is to avoid paying a supplier's invoice twice.