Good question. Everything is hypnosis and at the same time nothing is hypnosis. Most often it is understood as experiencing an altered state of consciousness.
A person may experience things differently than in a normal waking state, and their attention is directed inward.
Hypnosis is not sleep, although the external manifestations are similar to it in many ways.
Both in sleep and in hypnosis, a person has different brain wave frequencies, but they are distinct from each other.
You are in control the whole time and I am just guiding you.
With a few exceptions of "insidious", manipulative, hypnosis, it is not possible to "force" a person to do what they do not want to do.