Boygrouping denotes vvvvs built-in client-server architecture. It allows you to control any number of render computers (i.e. clients) from a single server. While you do all the patching only on the server vvvv takes care of all the connected clients to run n'sync Applications of boygrouping are usually multi-screen systems or seamless multi-projection setups.
In advanced setups it may be necessary that a client listens to multiple servers which can be achieved using MultiBoygrouping. But first make sure you understand the classic setup.