Reiki was discovered by Dr. Mikao Usui in the early 1900's. Techniques such as this have been practiced for thousands of years.
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, or there is a blockage or restriction in its flow then you are more likely to get sick or feel stress, and if it is high, we are more capable of being happy and healthy.
"Rei" means universal or everywhere and "Ki" means life energy or vital force. "Ki" also known as Chi, is also the primary energy of our emotions, thoughts and spiritual life and this life force is what leaves us when we depart.
Our energy plays such an important part in everything we do, it animates the body and has higher levels of expression.