Trademark fair use is defined in 15 U.S.C. 1115(b). Under this section, there are nine listed defenses to trademark infringement, but the most important one for purposes of this discussion is (b)(4), the so-called fair use defense to incontestability. Under 15 U.S.C. 1115(b)(4), a mark's incontestable status shall be subject to an alleged infringer's defense

"[t]hat the use of the name, term, or device charged to be an infringement is a use, otherwise than as a mark, of the party's individual name in his own business, or of the individual name of anyone in privity with such party, or of a term or device which is descriptive of and used fairly and in good faith only to describe the goods or services of such party, or their geographic origin;"

The fair use doctrine is somewhat analogous to the fair use doctrine of copyright law, which considers whether a defendant's use of copyrighted material is reasonable despite not having the copyright owner's permission to use the work, or is at least unlikely to negatively affect the copyright owner's economic interest in his copyright.