The process whereby infrastructure presents the same authentication credentials (or some other predetermined information or token) to a subsequent application, without the user re-entering it, or even being aware of it. This enables those third-party packaged applications that have their own built-in authentication that is not able to be detached, to behave as though they are participating in a Single Sign-on solution.

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