A Top-Level page is a container for a working set of screens and web pages your users can access. Your project can contain more than one Top-Level page, but must contain one at a minimum.
Your ASP.NET Web Application starts with a TopLevel web page. A TopLevel web page is one that can be accessed from an external resource (link, user Favorites entry) without any prior session information. Note that a toplevel page is not necessarily the first page a user might access; a Logon page will typically be generated as the default.aspx page any time users need to sign on with a userid and password to gain system access.
Top Level Page with ConnectionType = Logon Page