There are many things that make live rock LIVE. Live rock itself in my view is a rather general classification. For example if the rock is dry and has been stored dry then it should be classified as dead rock. If the rock has been stored in an active aquarium then more than likly the rock will be live. The degree a rock is alive will differ. Some live rock may just contain a good bactera population. Other live rocks will add varous pods
and worms to the bactera population. Usually the highest priced live rock will include varoius macro algae and may even some small coral frags on it.