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.
Voyeuristic practices may take a number of forms but its 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, peeping through an opening, and/or using techniques like binoculars, a mirror, camera (including camera phone and video camera), etc., and this stimulus 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 it may or may not be appreciated, depending on the other person(s) being exhibitionistic.
Non-consensual voyeurism is an invasion of privacy.
Voyeurism is considered a deviant sexual act and even a sex crime in most cultures, is most frequently practiced by males, and is tolerated to some degree in certain societies depending upon the circumstances (e.g., adolescent "Peeping Toms"). Sites such as Privatevoyeur.com and voyeurweb.com depict voyeurism as it is used and condoned in some societies.
In the United Kingdom, non-consensual voyeurism became a criminal offence on May 01, 2004, under the Sexual Offences Act 2003.
Some organizations and places have started to ban camera phones because of the privacy issues they raise, and to combat voyeurism, e.g. several gyms in the United States. One country, Saudi Arabia, has banned the sale of camera phones nationwide (although pilgrims on the hajj are allowed to bring in camera phones). Another, South Korea, requires that all camera phones sold in the country make a clearly audible sound whenever a picture is taken.