When a defendant uses a trademark to describe the plaintiff's product, even if his end goal is to describe his own product, he is entitled to a nominative fair use defense provided he meets the following three requirements:
- the product or service in question must be one not readily identifiable without use of the trademark;
- only so much of the mark or marks may be used as is reasonably necessary to identify the product or service; and
- the user must do nothing that would, in conjunction with the mark, suggest sponsorship or endorsement by the trademark holder.
This includes comparative advertising, but that is not the only scenario.