The astral body is the theoretical subtle or spiritual body, a third option between the eternal soul and the body (according to Platonic theory) though some believe that the astral body and the soul are equivalent. The astral body maintains your personality separate from your physical body, the mind and emotions, separate from the physical brain. Some refer to this body as the etheric body. The word “astral” means “of the stars”.
The astral body is often related to the aura. Some believe that the aura surrounding everything is their astral body, though there are many that disagree with this. The astral body is often reported as appearing identical to the physical body with the aura intact and more readily visible.
Functionally, the astral body is the part of you that travels during an out of body experience that are not near death experiences, such as astral projection. Many believe it is also the “dream self”, that part of you that moves around in dream space, though there are many that prefer a more solid division between dreams and astral activity.
Different cultures relate ideas similar to the astral body although different traditions identify different bodies. Neo-Platonic philosophy describes three bodies, the physical, the astral and the immortal soul while the ancient Egyptians described the body, the Kha, and the Ba, the immortal soul, symbolized by a bird. Theosophy describes seven spiritual parts1.
Body of Light by Juan Li
The Astral Body at Kheper.net
The Astral Body and other Astral Phenomena by A.E. Powell