The default domain is an application domain that is created
automatically by the CLR every time it is initialized in a process. The
default domain is not unloaded until the process shuts down. Most hosts
dont run code in the default domain for two main reasons. First, the
default domain cannot be shut down independently of the process.
Second, for security and isolation reasons, it is desirable that the
user code and hosting code execute in different application domains.
Instead, hosts create application domains with a set of properties that
control security, isolation, loading, etc.
Regards,
Satheesh