Claimant

A party whose identity is to be verified using an authentication protocol.
SOURCE: SP 800-63; FIPS 201

An entity which is or represents a principal for the purposes of authentication, together with the functions involved in an authentication exchange on behalf of that entity. A claimant acting on behalf of a principal must include the functions necessary for engaging in an authentication exchange. (e.g., a smartcard [claimant] can act on behalf of a human user [principal])
SOURCE: FIPS 196

An entity (user, device or process) whose assertion is to be verified using an authentication protocol.
SOURCE: CNSSI-4009