The separation of the the Soul or the Astral body from physical body and traveling to the Astral Plane or Astral Realm is called as Astral Projection.
The Astral Projection is one which is accounted worldwide in all religions as After Life in which the Astral body travels out of the physical body to attain higher realms , Everyone leave their physical body and travels through their Astral body every night when asleep, but most of the people don't remember this.
When the physical mind is asleep, the subconscious takes over the control, this is the point where you Astral project , In general the Astral projection is done by everyone, but only some people can remember it, most of the people don't remember it.
The Astral Projection is an Ancient Art which everyone should learn to attain inner awakening.