A beautiful way of describing Reiki is a transaction of love. The reiki partitioner sends loving energy to the reiki receiver. However in more scientific words it is a Japanese technique to release stress and support relaxation. It also promotes healing.
Getting a Reiki treatment feels like going into a deep meditation. Where your mind, your body and your soul come together. You might feel slight vibrations in your body or thoughts and emotions come up. It may release you from stress or traumas and could connect you closer to your inner being.
Reiki is getting more an more acknowledged as a beautiful way for healing. The best way to enter a session is with an open mind and without any expectations.