What does 'return *this' mean in C++?

What does 'return *this' mean in C++?

I'm converting a C++ program to C#, but this part has me confused. What
does return *this mean?
template< EDemoCommands msgType, typename PB_OBJECT_TYPE >
class CDemoMessagePB : public IDemoMessage, public PB_OBJECT_TYPE
{
(...)
virtual ::google::protobuf::Message& GetProtoMsg() { return *this; }
}
How would it translate into C#?