(b) defenses

To the extent that the right to use the registered mark has become incontestable under section 1065 of this title, the registration shall be conclusive evidence of the validity of the registered mark and of the registration of the mark, of the registrant’s ownership of the mark, and of the registrant’s exclusive right to use the registered mark in commerce. . . . Such conclusive evidence of the right to use the registered mark shall be subject to proof of infringement as defined in section 1114 of this title, and shall be subject to the following defenses or defects:

....

(4) That 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...

....

(from Cornell’s copy of 15 USC § 11115)