Answer:   An application domain is a logical isolation boundary created around . NET applications so that applications do not access or affect each other. It is a light-weight process having its own set of code, data, and configuration settings.

How does application domain work -
If you run code in 2 different AppDomains within a process, the code will run in isolation. Any communication between the AppDomains will get either serialized or handled via MarshallByRefObject. It behaves very much like using remoting in this regard. This provides a huge amount of security - you can run code that you don't trust, and if it does something wrong, it will not affect you.

Answer:   Windows Operating Systems load a set of resources like .EXE, DLLs and allocate the memory for those resources in an area called as Process. Windows OS creates a separate and isolated area for each running application. Making separate isolation area for each application, makes the process more secure and stable. In case, one process fails, it does not affect the other process.
.NET applications, however, are not hosted like traditional applications by Windows Operating System. Under .NET, .EXEs are hosted under a process by logical partitioning which is known as "Application Domain". Now you can host multiple application domains under one single process.


Application Domains consume less memory and power for processing the applications compared to the traditional processes for each application. In case one application domain fails, the other application domain will work as-is without any effects. You can also stop one application domain without affecting another application domain or without stopping an entire process.
One Application Domain cannot share/access the data from other Application Domain which is running within the same Domain or other Domain.