Voyeurism

Voyeurism is the sexual interest in or practice of spying on people engaged in intimate behaviors, such as undressing, sexual activity, or other actions usually considered to be of a private nature. The principal characteristic of voyeurism is that the voyeur does not normally interact directly with the subject of his/her interest, who is often unaware of being observed. The essence of voyeurism is the observing but may also involve the making of a secret photograph or video of the subject during an intimate activity. When the interest in a particular subject is obsessive, the behavior may be described as stalking. Source: Wikipedia