Voyeurism
Voyeurism is a practice in which an 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. The word derives from French verb voir (to see) with the -eur suffix that translates as -er in English. A literal translation would then be “seer” or "observer", with pejorative connotations. Also, the word voyeur can define someone who receives enjoyment from witnessing other people's suffering or misfortune.
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.
The key element behind voyeurism, and the factor that distinguishes it from mixoscopia (pleasure from watching others have sex), is that those watched are unaware of the voyeur. Part of the thrill of voyeurism may lie in almost being caught. For some, the closer the voyeur is to being discovered, the larger the thrill. This form of non-consensual voyeurism is considered an invasion of privacy.
Voyeurism may be tolerated or even appreciated if the people viewed are exhibitionists. This relationship is typically role-play where the exhibitionist pretends to not know of the voyeur's presence.
A subset of voyeurs derive sexual pleasure from looking under articles of clothing, an act known as an upskirt. This can be accomplished by camera or simply by a chance viewing up skirts. Some voyeurs also derive pleasure by looking down shirts and viewing breasts, particularly when a woman is bending over. This is commonly referred to as a downblouse.
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Silly NTs, I have Aspergers, and having Aspergers is gr-r-reat!