Hypnosis is a mental state (according to “state theory”) or imaginative role-enactment (according to “non-state theory”). It is usually induced by a procedure known as a hypnotic induction, which is commonly composed of a long series of preliminary instructions and suggestions. Hypnotic suggestions may be delivered by a hypnotist in the presence of the subject, or may be self-administered (“self-suggestion” or “autosuggestion”). The use of hypnotism for therapeutic purposes is referred to as “hypnotherapy“, while its use as a form of entertainment for an audience is known as “stage hypnosis”.
The words hypnosis and hypnotism both derive from the term neuro-hypnotism (nervous sleep) coined by the Scottish surgeon James Braid around 1841. Braid based his practice on that developed by Franz Mesmer and his followers, but differed in his theory as to how the procedure worked.
Contrary to a popular misconception – that hypnosis is a form of unconsciousness resembling sleep – contemporary research suggests that hypnotic subjects are fully awake and are focusing attention, with a corresponding decrease in their peripheral awareness. Subjects also show an increased response to suggestions. In the first book on the subject, Neurypnology (1843), Braid described “hypnotism” as a state of physical relaxation accompanied and induced by mental concentration (“abstraction”).
Definition courtesy Wikipedia.