Voyeurism refers to a Psychosexual Disorder in which a person derives sexual pleasure, Arousal and gratification from looking and observing unsuspecting persons undressing or naked and genital organs or observing the sexual acts/activities of others.
The voyeur is usually hidden from view of others. Voyeurism is a form of paraphilia.
A variant form of Voyeurism involves listening to erotic conversations, commonly referres as telephone sex, although it is usually considered voyeurism primarily in the instance of listening to unsuspecting persons.
Other /More definition:
Voyeurism is looking at people while they are undressing or having sex, without their knowledge. It is the obtainment of sexual arousal by compulsively and secretly watching another person undressing, bathing, engaging in sex, or being naked
Lexicon of Psychology - Terms, Treatments, Biographies,