The ability through historical logs and logical analysis to prevent or discourage an Entity from denying that it had acted as an Identity in a given transaction, especially in a legal sense. It may need to be based on a biometric and include encrypted audit trails to be successful in a court of law; otherwise the offender could be able to plead guilty to the lesser charge of leaving their password on a Post-It Note.

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