Definition of Anonymous User in The Network Encyclopedia.
What is an Anonymous User?
Anonymous User is any user who accesses network resources without providing a username or password.

Some Microsoft Windows Server applications like Microsoft Internet Information Services (IIS) can be configured to allow anonymous users to access their resources. This allows distrusted users from unsecured networks such as the Internet to access data that is made available for the public at large.
How it works
Access to network resources by anonymous users can be controlled by assigning permissions to a special anonymous user account. Windows Operating Systems then provides anonymous users access to resources by impersonating the user utilizing the anonymous user account. When a user visits a web page without a login, that’s an anonymous user.