37 C.F.R. § 41.60
In addition to the definitions in § 41.2 , the following definitions apply to proceedings under this subpart unless otherwise clear from the context:
Appellant means any party, whether the owner or a requester, filing a notice of appeal or cross appeal under § 41.61 . If more than one party appeals or cross appeals, each appealing or cross appealing party is an appellant with respect to the claims to which his or her appeal or cross appeal is directed.
Filing means filing with a certificate indicating service of the document under § 1.903 of this title.
Owner means the owner of the patent undergoing inter partes reexamination under § 1.915 of this title.
Proceeding means an inter partes reexamination proceeding. Appeal to the Board in an ex parte reexamination proceeding is controlled by subpart B of this part. An inter partes reexamination proceeding is not a contested case subject to subpart D.
Requester means each party, other than the owner, who requested that the patent undergo inter partes reexamination under § 1.915 of this title.
Respondent means any requester responding under § 41.68 to the appellant's brief of the owner, or the owner responding under § 41.68 to the appellant's brief of any requester. No requester may be a respondent to the appellant brief of any other requester.
37 C.F.R. §41.60