Article on Quackwatch, the website that watches out for "quacks", or scams:

Reiki is one of several nonsensical methods commonly referred to as "energy healing." These methods are based on the idea that the body is surrounded or permeated by an energy field that is not measurable by ordinary scientific instrumentation. The alleged force, said to support life, is known as ki in Japan, as chi or qi in China, and as prana in India. Reiki practitioners claim to facilitate healing by strengthening or "balancing" it [1].

In a traditional reiki session, the client lies down or sits fully clothed. The practitioner's hands are placed lightly on or just above the client's body, palms down, using a series of 12-15 positions. Each position is held for about 2 to 5 minutes, or until the practitioner feels that the flow of energy—said to be experienced as sensations such as heat or tingling in the hands—has slowed or stopped. Typically, the practitioner delivers at least four sessions of 30 to 90 minutes each. The techniques include "/home/hrefs/public_html/centering," "clearing," "beaming," "extracting harmful energies," "infusing," and "smoothing and raking the aura," all of which are claimed to influence the imaginary "energy" that Reiki advocates postulate.

Reiki can also be self-administered or administered to others at distant locations. Some practitioners say that "spirit guides" help them produce the proper flow of energy.

(via "Reiki Is Nonsense", Quackwatch, by Stephen Barrett, M.D., click link to read more)