peeping Tom

Definition from Nolo’s Plain-English Law Dictionary

A person who stealthily peeks into windows, holes in restroom walls, or other openings with the purpose of seeing people undressed or couples making love. The term comes from the legendary Tom who peeked when Lady Godiva rode her horse naked through the streets of Coventry to protest taxes. Being a peeping Tom is treated as a crime based on sexual deviancy, and a victim may sue a peeping Tom for invasion of privacy.

Definition provided by Nolo’s Plain-English Law Dictionary.