Voyeurism is a practice in which the individual derives sexual pleasure from observing other people. Such people may be engaged in sexual acts, or be nude or in underwear, or dressed in whatever other way the "voyeur" finds appealing. Two actorsYoung girl watches secretly while two male actors make love. Silk painting; China, Qing Dynasty.

Voyeuristic practices may take a number of forms but their characteristic feature is that the voyeur does not directly interact with the object of their voyeurism (often unaware that they are being observed), instead observing the act from a distance by peeping through an opening or using aids such as binoculars, mirrors, cameras (including camera phones and video cameras), etc. This stimulus sometimes becomes part of a masturbation fantasy during or after the observation.

Some voyeurs derive sexual pleasure from looking up skirts or trousers, known as an upskirt. This can be accomplished by camera or simply by a chance viewing when a person sits down. Some voyeurs also derive pleasure by looking down shirts and viewing breasts, particularly when a person is bending over. This is commonly referred to as a downblouse.

When done openly, voyeurism may be tolerated or even appreciated, especially if the person(s) viewed is/are exhibitionist. However, non-consensual voyeurism is an invasion of privacy.

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