instance of an instance? group instance?

I just want to be clear, lets say I have two objects lets say a plane and a cylinder.

I add a particle system to the plane ( hair) and I used the cylinder as an instance. Ok I go that.

so what if I want instance that plane with the instances on it?, is that what a group instance is? It will only calculate the original plane once, and I can do as many group instances as I want?

thanks in advance.

Sure, why not? These are the kinds of things you can just try out yourself to see if they work or not.