Reiki For Holistic Health.com:
The electromagnetic field that surrounds the human body (Human Energy Field-HEF) and every organism and object in the Universe.The Human Energy Field as a collection of electro - magnetic energies of varying densities that permeate through and emit or exit from the physical body of a living person. These particles of energy are suspended around the healthy human body in an oval shaped field.
The author then describes each of the 7 layers of the aura (physical, etheric, vital, astral, lower mental, higher mental and spiritual).
Ellie Crystal's Crystalinks (this site has interesting graphics of auras):
In metaphysics, Aura refers to the energy field emanating from the surface of a person or object. This emanation is visualized as an outline of cascading color and may be held to represent soul vibrations, chakric emergence, or a reflection of surrounding energy fields.
Modern New Age metaphysics identify the aura as electromagnetic fields. The existence of electromagnetic fields around every object in the known world is a scientifically proven fact. What is debatable is whether or not humans can see these electromagnetic fields as colors with the naked eye. This claim is considered paranormal because devices that sense electromagnetic fields at magnitudes many times smaller than that which allegedly exists in auras have recorded nothing. However, these energy fields are sometimes claimed to be documented by a rare form of photography called Kirlian photography.
In parapsychology and many forms of spiritual practice, an aura is a field of subtle, luminous radiation supposedly surrounding a person or object like the halo or aureola of religious art. The depiction of such an aura in religious art usually connotes a person of particular power or holiness. According to the literature of Theosophy, Anthroposophy, and Archeosophy, each color of the aura has a precise meaning, indicating a precise emotional state.