Live rock to me is cycled, has nitrifying bacteria and other organic life. Dry rock is un-cycled uncured rock devoid of life. Some nowadays say manmade rock is dry where as pukani, Fiji, or Tonga rock is live to me if it has no life its not live though.
In my mind it is really a spectrum. As soon as dry rock goes into a tank it starts becoming "live". Within days/weeks it can become "live" enough for converting ammonia/nitrites so some may call that "live" rock. I dont consider it good live rock until much longer than that as it matures. I find a big difference between cycled dry rock and established love rock that has been in a system for several months/years.