An aura is a subtle field of luminous multicolored radiation surrounding a person or object as a cocoon or halo. An aura may be held to represent or be composed of soul vibrations or chakras, and may reflect the moods or thoughts of the person it surrounds.1
Aura photogaph taken with Kirlian Camera
(Post-edited to blur face)
There are people who can see auras naturally and there are others who believe that everyone can be trained to see auras. People who can see auras often describe that auras extend a few inches to a few feet from our physical bodies. However, it can extend to many times more for a highly spiritual person.
Auras are composed of every imaginable colour and these colours change as a person's emotional, physical and mental states change. For example, purple indicates spiritual thoughts; green is a healing color; and red can mean anger or power.
You can also find out about your aura colours through kirlian photography.
Auras are also thought to be your energy bodies. Other terms are light body, astral body, causal body, mental body and etheric body, etc.
1 Quoted from wikipedia: http://en.wikipedia.org/wiki/Aura_(paranormal)
Further reading:
http://www.esolibris.com/articles/auras_chakras/aura_color.php
