An Application Domain is a logical container for a set of assemblies in which an executable is hosted.Application Domains, each of which is hosting a .NET executable. The first appdomain created when the CLR is initialized is called the default AppDomain and this default one is destroyed when the Windows process is terminated.
An AppDomain can be independently secured.
An AppDomain can be unloaded.
Independently configured.
No mutual intervention by multiple appdomains.
Performance