47 CFR § 73.3511 - Applications required.
(a) Formal application means any request for authorization where an FCC form for such request is prescribed. The prescription of an FCC form includes the requirement that the proper edition of the form is used. Formal applications on obsolete forms are subject to the provisions of § 73.3564 concerning acceptance of applications and § 73.3566 concerning defective applications.
(b) Informal application1 means all other written requests for authorization. All such applications should contain a caption clearly indicating the nature of the request submitted therein.
(c) Formal and informal applications must comply with the requirements as to signing specified herein and in § 73.3513.