What are lucid dreams? They are usually defined as a dream in which you know you are dreaming, that is, you can consciously state to yourself that you are in a dream. As in, “hey, I’m in a dream now, this is pretty cool. Let’s see if I can fly!” and then … whoosh! … you’re off into the air, flying in your dream.
Astral travel is having a similar experience although usually, unless you are travelling in one of the astral planes, it is assumed that astral travelling occurs in the same reality your physical body inhabits during waking life. This has not been proven and some think astral travel is just a form of lucid dreaming.
A waking dream is a good way of looking at astral travel. The vividness of dreams with the conscious control of the waking state combined into one.