Astral projection is a generic term for an "out of body experience" (OOBE) common to many occult and spiritual disciplines whereby the "consciousness" of a person leaves the physical or corporeal body and apparently travels either within the physical world independent of the corporeal body or to other non-physical realms. Astral Projection as a generic term includes such specific phenomena as lucid dreaming and the mystical exercise referred to as Rising on the Planes.
Astral Projection as a phenomenon
As a spiritual experience, astral projection may even be referenced in the Christian/Jewish Bible: "Remember [your Creator] — before the silver cord is severed,
  or the golden bowl is broken;   before the pitcher is shattered at the spring,   or the wheel broken at the well,   and the dust returns to the ground it came from,   and the spirit returns to God who gave it."  —Ecclesiastes 12:6.
The verse refers to an observation common to many manifestations of astral projection: that the "astral body" (the part of consciousness that leaves the corporeal body) is connected to the physical body by a silver or golden cord. Some disciplines teach that if this cord is severed, the soul will separate from the body and physical death or coma will result.
The process of astral projection is usually fairly simple: the practitioner enters a state of relaxation, usually through meditation, sometimes aided by music, chanting or, less frequently, by drugs; he or she envisions a double of his or her body next to the position he or she is in; he or she then transfers her senses and consciousness to the visualized double—the astral body, or Body of Light, as Crowley called it, and the astral body then travels wherever the practitioner wants it to go.
Thelemic Astral Projection: The Body of Light
Aleister Crowley strongly advocates traveling in the Body of Light as one of the fundamental tools of Thelema. Chapter XIII of Magick in Theory and Practice describes in detail with "The Body of Light, Its Power and Development" and contains practical instruction on forming the Body of Light:
The first thing to do, therefore, is to get the body outside your own. To avoid muddling the two, you begin by imagining a shape resembling yourself standing in front of you. Do not say: "Oh, it's only imagination!" The time to test that is later on, when you have secured a fairly clear mental image of such a body. Try to imagine how your own body would look if you were standing in its place; try to transfer your consciousness to the Body of Light. Your own body has its eyes shut. Use the eyes of the Body of Light to describe the objects in the room behind you. Don't say. "It's only an effort of subconscious memory" ... the time to test that is later on.
Most rituals described by Crowley are to be done in the Body of Light, as are many other inititation rites. Indeed, Crowley admonishes Thelemites to "[t]ravel also much in the Empyrean in the Body of Light, seeking ever Abodes more fiery and lucid" in Liber Aleph. So the practicing Thelemite must master "astral projection"—travel in the Body of Light—as an essential method in discovery of his or her True Will, a method "easy, agreeable, not tedious, and in the end...certain..." (Liber CL, De Lege Libellum)
