Net 30 is a form of Trade Credit which specifies payment is expected to be received in full 30 days after the goods are delivered. Net 30 terms are often provided with associated "credits" that are given for early payment; e.g. 2% 10, Net 30 indicates a 2% discount is provided if payment is received within 10 days of the delivery of goods, and that full payment is expected within 30 days.
