The process of an entity (re)establishing an Identity with a service provider. For example; a bank's 100-point check, an employment background check, an RA process for generating a Digital Certificate. Usually results in the issuing of a Credential that is associated with the Identity. Registration strength also has a time value, in that recent registrations may provide a greater assurance than old registrations (re-registration will uncover any errors, expiries and changes). Not to be confused with the "registration" of a device.

Source: http://identityaccessman.blogspot.com/2006/08/identity-dictionary.html