The process of discovering the identity (i.e., origin or initial history) of a person or item from the entire collection of similar persons or items.
Sources:
FIPS 201-3 under Identification

  The process of discovering the true identity (i.e., origin, initial history) of a person or item from the entire collection of similar persons or items.
Sources:
CNSSI 4009-2015
NIST SP 800-79-2 under Identification

  The process of verifying the identity of a user, process, or device, usually as a prerequisite for granting access to resources in an IT system.
Sources:
NIST SP 800-82 Rev. 2 under Identification

  The bit string denoting the identifier associated with an entity.
Sources:
NIST SP 800-56B Rev. 2 under ID

  The process of using claimed or observed attributes of an entity to single out the entity among other entities in a set of identities.
Sources:
NIST SP 800-188 from ISO/TS 25237:2008

  process of using claimed or observed attributes of an entity to single out the entity among other entities in a set of identities
Sources:
NISTIR 8053 from ISO/TS 25237:2008

  A unique, auditable representation of identity within the system usually in the form of a simple character string for each individual user, machine, software component or any other entity.
Sources:
NISTIR 5153 under Identification