Astral Travel or the Out of Body experience is the separation of consciousness from the physical body to the non physical or astral body. When Astral traveling one usually can look at the physical body that was just left. For instance standing at the foot of your bed and seeing yourself sleeping in it. The astral body is the minds expectation and self concept.  An overweight person may see themselves as thin and young in the unconscious state.
The difference between dreams and the out of body experience is that dreams are like a rapid projection of a motion picture without awareness or control.  When having an out of body experience you are self aware and can consciously control your movements.

When sleeping and beginning the out of body experience with a command like “I am out of my physical body now” or “clarity now”,  or other such affirmations, one feels a numbness and a vibration throughout the body and leaves when the unconscious mind leaves the physical body. During the beginning of the separation full conscious control is important as the nonphysical state of consciousness responds to the slightest thought. If a person is frightened or thinks about the physical body, consciousness returns to the physical body.

The out of body experience can be obtained by practice and familiarity or induced by listening to a series of frequencies that mimic the vibrations that your body emits when beginning the separation from the physical to the non physical consciousness. Astral traveling is not observing the physical world from a different perception but interaction on a separate but parallel dimension of energy.