Reiki is a Japanese technique for stress reduction and relaxation that also promotes healing. It is administered by "laying on hands" and is based on the idea that an unseen "life force energy" flows through us and is what causes us to be alive. If one's "life force energy" is low, then we are more likely to get sick or feel stress, and if it is high, we are more capable of being happy and healthy. (As described by ICRT)
Reiki was discovered by Mikao Usui in 1922 whilst performing a twenty-one day retreat on Mount Kurama, involving meditation, fasting and prayer. Usui said that by mystical revelation, he had gained the knowledge and spiritual power to apply and attune others to what he called Reiki.
There are three forms of degrees, commonly referred to as the First, Second, and Master/Teacher degree. At First Degree, a Reiki practitioner is able to heal themselves and others, at Second Degree is able to heal others distantly (commonly called distant healing) with the use of specialized symbols, and at Master/Teacher level is able to teach and attune others to Reiki.