Red Light District, Amsterdam, Netherlands

A red-light district is a neighborhood or a part of a neighborhood where businesses connected to the sex industry (sex shops, strip clubs, adult theaters etc.) exist. In some red light districts, prostitution may legally take place; other red light districts are known for their illegal prostitution scene. The term "red-light district" was first recorded in the United States in 1894, in a newspaper article in The Milwaukee Sentinel of Wisconsin. Other mentions from the 1890s are numerous, from locations all over the United States.
In the 19th century, the term "red light" was associated with the red lanterns carried by railway workers (which the latter left outside brothels when they entered).