.NET Remoting : What is Marshalling objects by reference?

Marshaling by reference is analogous to having a pointer to the
object. Marshal by reference passes a reference to the remote object
back to the client. This reference is an ObjRef class that contains
all the information required to generate the proxy object that does
the communication with the actual remote object. On the network, only
parameters and return values are passed. A remote method invocation
requires the remote object to call its method on the remote host
(server).

Marshal by reference classes must inherit from System.MarshalByRefObject.