14 CFR § 21.601 - Applicability and definitions.
(a) This subpart prescribes -
(1) Procedural requirements for issuing TSO authorizations;
(2) Rules governing the holders of TSO authorizations; and
(3) Procedural requirements for issuing letters of TSO design approval.
(b) For the purposes of this subpart -
(4) An article manufactured under a TSO authorization, an FAA letter of acceptance as described in § 21.613(b), or an article manufactured under a letter of TSO design approval described in § 21.621 is an approved article for the purpose of meeting the regulations of this chapter that require the article to be approved; and
(5) An article manufacturer is the person who controls the design and quality of the article produced (or to be produced, in the case of an application), including any related parts, processes, or services procured from an outside source.