To explain what hypnosis is, it might be better to state what hypnosis is not.
When a person is hypnotized, they are not asleep or in some eerie trance state. The hypnotized individual is aware of everything that is taking place. Even after being brought out of hypnosis, a person will be able to recall anything that took place during the session.
Hypnosis is a very normal, natural state that most of us experience every day. An example of daily hypnosis would be driving a car and realizing that you can't remember the last three or four streets you just passed. Perhaps you drove right by your exit! Another example would be a person watching television. When another member of the family enters and announces that dinner is ready, the person watching the television did not even blink an eye!
These are examples of a light hypnotic state. In both cases the conscious part of the mind had been distracted, allowing the subconscious part of the mind to take over.