Yūkaku (遊廓) meant the regions in Japan where brothels recognized by the government were situated. In theory, prostitution was legal only in the Yūkaku region, but there were some places where prostitution was provided illegally (e.g. Okabasho 岡場所).
In January 1946, GHQ issued an order (SCAPIN 642) nationwide to abolish Japan's licensed prostitution system, and the brothels in Yūkaku had to change their name to café (カフェ) or ryōtei (料亭 (りょてい)), which transformed the Yūkaku into Akasen (赤線) regions.
After the Anti-Prostitution Law (売春防止法 baishun bōshi hō) was enforced in 1956, prostitution became banned in Japan, and as such the Yūkaku finally came to an end, though illegal prostitution still continues in Japan.