Reiki has been defined in traditional terms as Universal Life Force.  The word can be broken down into Rei...

"Research into the esoteric meaning of the Japanese kanji character for Rei has given a much deeper understanding of this ideogram. The word Rei as it is used in Reiki is more accurately interpreted to mean higher knowledge or spiritual consciousness. This is the wisdom that comes from God or the Higher Self and is the God-Consciousness which is all-knowing. It understands each person completely. It knows the cause of all problems and difficulties and knows how to heal them..."

and ki

"It is the God-Consciousness called Rei that guides the energy called Ki in the practice we call Reiki. Therefore, Reiki can be defined as spiritually guided life energy" - William Lee Rand, Reiki the Healing Touch

During a Reiki session, the client lies on a message table, fully clothed, while the Reiki practitioner places his or her hands on or near the client's body. The Reiki energy flows from the universal Reiki source to the practitioner, and through the practitioner to the client. The Reiki energy knows what is needed and where it is needed. Since the God-consciousness and not the mind of the practitioner direct the energy, it can never do harm.

The experience of the client varies greatly from person to person and from time to time for the same person. You may expect to feel deeply relaxed and centered after a Reiki session. It may be a profound spiritual experience, a super nap, or just a pleasant time of relaxation. You may have images come to mind, or experience feelings or emotions.

Clients often report that pain is diminished or gone after a Reiki session even if the practitioner did not know that the pain existed.

Many people feel heat or the vibrational energy from the practitioner's hands.

Reiki can help relieve physical and emotional pain, promote spiritual clarity, speed the healing process and balance the body's energy.