"The word Reiki is made of two Japanese words - Rei which means "God's Wisdom or the Higher Power" and Ki which is "life force energy". So Reiki is actually "spiritually guided life force energy." (This from www.reiki.org)
This question is brought up a lot by people who wonder what I mean when I suggest that I can "do Reiki" to help ease pain, frustration, promoting healing or even to help solve a problem. It is not "I" doing the work, but the Great I Am within me directing me. I've been trained as a Level III Reiki Master and been practicing since 1997. I was inducted by Kaimora, a Reiki teacher who worked in an area near Rangeley, Maine and in St. Augustine, Florida.
I sit and focus on the name, photograph or simply the energy of an individual or situation and allow myself to be the channel for that energy to come through to be used by that person or situation for the highest and best good. If that individual isn't ready to receive the energy, it just washes over them - no harm, no blame. If they are receptive, it goes where it is most needed.
When I can actually be present with someone to do healing work, I have heard comments like, "Your hands are putting off a lot of heat," or "I can feel tingling when your hands are near that spot." I don't actually touch... some Reiki Masters may, but I have better results keeping my hands about 2 inches away from the body.
It is also a useful practice for healing animals. I had a cat that had seizures once a month and the vet was offering me a chance to spend a lot of money while he "investigated" the problem. I sat down with the cat and asked her how I could help and then we agreed that I could send her Reiki on her schedule - cats are like that. In a few months she had no more episodes.
My objective in offering up my time for this healing work is to be of service. I have no offices, no forms to fill out, and I do not charge anyone to "put the energy out there" for their needs or that of their loved ones. I have a relative who is dealing with Multiple Myeloma and so one of my offerings is to send energy out to the various MM bloggers... one might say I am like a water fountain where anyone who is thirsty may come and have a drink. Since the energy is there, free for the taking, it can be "captured" or it just goes on flowing on its own.
It is a great practice to work on being "of the world" but not "in the world."