The common language runtime exposes COM objects through a proxy called the runtime callable wrapper (RCW). Although the RCW appears to be an ordinary object to .NET clients, its primary function is to marshal calls between a .NET client and a COM object.
Runtime Callable Wrapper
The runtime creates exactly one RCW for each COM object, regardless of the number of references that exist on that object. The runtime maintains a single RCW per process for each object. If you create an RCW in one application domain or apartment, and then pass a reference to another application domain or apartment, a proxy to the first object will be used. As the following illustration shows, any number of managed clients can hold a reference to the COM objects that expose INew and INewer interfaces.
http://msdn.microsoft.com/en-us/library/8bwh56xe(v=vs.110).aspx
