According to http://msdn.microsoft.com/en-us/library/ms175475.aspx

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A database user for which the corresponding SQL Server login is undefined or is incorrectly defined on a server instance cannot log in to the instance. Such a user is said to be an orphaned user of the database on that server instance. A database user can become orphaned if the corresponding SQL Server login is dropped. Also, a database user can become orphaned after a database is restored or attached to a different instance of SQL Server. Orphaning can happen if the database user is mapped to a SID that is not present in the new server instance.

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Both, users with wrong sid and users without login, no matter whether droped or just not exist after restore, are orphaned users