It’s pretty simple. Hypnosis is using the power of the mind to influence a person’s reality. While traditionally a hypnotist would do an induction to put a subject into trance, hypnosis can take place with or without trance ensuing, while inductions can be overt or covert. So how would you know if it were happening to you?
I have the power. You have the mind I will be influencing. See how it works?