17 U.S.C. § 1501

In this chapter— (1) the term “claimant” means the real party in interest that commences a proceeding before the Copyright Claims Board under section 1506(e), pursuant to a permissible claim of infringement brought under section 1504(c)(1), noninfringement brought under section 1504(c)(2), or misrepresentation brought under section 1504(c)(3); (2) the term “counterclaimant” means a respondent in a proceeding before the Copyright Claims Board that— (A) asserts a permissible counterclaim under section 1504(c)(4) against the claimant in the proceeding; and (B) is the real party in interest with respect to the counterclaim described in subparagraph (A); (3) the term “party”— (A) means a party; and (B) includes the attorney of a party, as applicable; and (4) the term “respondent” means any person against whom a proceeding is brought before the Copyright Claims Board under section 1506(e), pursuant to a permissible claim of infringement brought under section 1504(c)(1), noninfringement brought under section 1504(c)(2), or misrepresentation brought under section 1504(c)(3).