The word or rather term Reiki comes from a combination of the Japanese words
Rei - 霊 and Ki - 気 which
together translate as "Universal Spirit" and "Life Force". In English it is often called Universal Life Force Energy.
Some say Reiki originated in Tibet, others say it came from India originally. While others insist that Reiki was original
to Dr. Usui and there was nothing like it before.
Truth is, they are all correct. In ancient times the healers from just about every culture knew intuitively how to access
and channel the Universal Life Force energy which is exactly what a Reiki practitioner does. So in this sense one could say
it originated in a variety of ancient cultures. And then this ability was later rediscovered by Mikao Usui in the early 1900's
as a method of accessing the natural Healing Energy that surrounds us.
Then again, once Dr. Usui found that he could access this healing energy he formed a structure around it. He invented the
way to teach it, he formed a philosophy around it and he was the one to name his specific practice "Reiki" so, in this sense,
it was indeed invented by him.