Impersonation is the capability for the ASP.NET process to run in the context of a particular user identity. It is said to “impersonate” the logged-in user and is capable of using the logged-in user's identity to act on the user's behalf.
By default, Impersonation is not enabled in ASP.NET. You might initially doubt this because if you look at the User.Identity.Name property with Windows authentication enabled, it will be set to the logged-in user. This, however, is not the identity that the ASP.NET application is using to access resources. The identity that is shown here is used during URL authorization and file authorization, but will not be used as the identity when calling other base class functionality.