Это для домена приложения, как доказано в этом примере:
public class Foo
{
public static string Bar { get; set; }
}
public class Test
{
public Test()
{
Console.WriteLine("Second AppDomain: {0}", Foo.Bar);
}
}
class Program
{
static void Main()
{
// Set some value in the main appdomain
Foo.Bar = "bar";
Console.WriteLine("Main AppDomain: {0}", Foo.Bar);
// create a second domain
var domain = AppDomain.CreateDomain("SecondAppDomain");
// instantiate the Test class in the second domain
// the constructor of the Test class will print the value
// of Foo.Bar inside this second domain and it will be null
domain.CreateInstance(Assembly.GetExecutingAssembly().FullName, "Test");
}
}