Lucid dream is when you are aware in your dream... contrary to just watching yourself do stuff....... basicly know you're dreaming... once you realize that this is a dream you literally become "lucid" conscious in your dream and then you can do whatever you want... because if you dont become "lucid" and realize that you are dreaming... you will be stuck with the impression that this is real and you will be dragged by the currents of the sleeping mind.