48 C.F.R. § 204.7101
Accounting classification reference number (ACRN) means any combination of a two position alpha/numeric code used as a method of relating the accounting classification citation to detailed line item information contained in the schedule.
Attachment means any documentation, appended to a contract or incorporated by reference, which does not establish a requirement for deliverables.
Definitized item, as used in this subpart, means an item for which a firm price has been established in the basic contract or by modification.
Exhibit means a document, referred to in a contract, which is attached and establishes requirements for deliverables. The term shall not be used to refer to any other kind of attachment to a contract. The DD Form 1423, Contract Data Requirements List, is always an exhibit, rather than an attachment.
Nonseverable deliverable, as used in this subpart, means a deliverable item that is a single end product or undertaking, entire in nature, that cannot be feasibly subdivided into discrete elements or phases without losing its identity.
Undefinitized item, as used in this subpart, means an item for which a price has not been established in the basic contract or by modification.
48 C.F.R. §204.7101