Here are some words that I've seen mis-defined all around the Internet:
Scientology n. A religious practice developed by L. Ron Hubbard which applied to man's spirit and his spiritual freedom. It is the study and handling of the spirit in relationship to itself, universes and other life.
The word Scientology comes from Latin scio which means knowing in the fullest sense of the word and Greek logos, study of. In itself the word Scientology means "knowing how to know". Scientology is a route, a way rather than a dissertation or an assertive body of knowledge. Through its drills and studies, one may find the truth for himself. The technology is therefore not something to believe, but something to do.
(as excerpted from The Creation of Human Ability, Scientololgy 8-8008, Scientology, the Fundamentals of Thought, Scientology 0-8: The Book of Basics and other writings by L. Ron Hubbard.)
Dianetics n. A methodology developed by L. Ron Hubbard to address and handle the effects of the spirit on the body. Its application can help alleviate such ailments as unwanted sensations and emotions, irrational fears and psychosomatic illnesses.
Dianetics comes from the Greek word dia, meaning through and nous, meaning soul.
It is most accurately described as "what the soul is doing to the body through the mind".
(as excerpted from Dianetics: The Modern Science of Mental Health, Handbook for Preclears, Scientology, the Fundamentals of Thought, and other writings by L. Ron Hubbard)
Thetan n. The person himself - not his body or his name or his mind or anything else; that which is aware of being aware; the identity which is individual. The term was coined to eliminate any possible confusion with older, invalid concepts. It comes from the Greek letter theta, which the ancient Greeks used to represent thought or perhaps spirit, to which an "n" is added to make a noun in the modern style. It is also "theta to the nth degree", meaning unlimited or vast.
(as excerpted from The Creation of Human Ability, Scientololgy 8-8008, Book of Case Remedies and other writings by L. Ron Hubbard)
Mind n. A communication and control system between the thetan and his environment. The mind is a network of communications and pictures, energies and masses which are brought into being by the activities of the thetan versus the physical universe or other thetans. It is not the brain. It is everything used as part of the individual's thinking process, plus the thetan. A mind has to be alive to be considered a mind. Thus, a computer or electronic brain cannot be a mind; it can only be a thinking machine, as there is no life connected to it.
(as excerpted from Handbook for Preclears, Scientology, the Fundamentals of Thought, and other writings by L. Ron Hubbard)
An easy way to prove the difference between the brain, the mind and the thetan is: Think of a cat (you actually have to try this now...). So, you've got a picture of a cat? Who's looking at it? Where is it located?
Let me know what happens when you do the above.