An installment contract is a single contract that is completed by a series of performances–such as payments, performances of a service, or delivery of goods–rather than being performed all at one time. Installment contracts can provide that installments are to be performed by either one or both parties.
Tax Deferral (for the seller): One of the most compelling reasons to consider an installment sale is the ability to defer capital gains tax.
About Form 9465, Installment Agreement Request. Internal Revenue Service.