Ukiyo (oo-kee-yoh)

Ukiyo is an ancient term which was once used by the adherents of the Eightfold Path of Creation's Dawn to describe the living world. During the height of the Age of Bushi, when a nominal peace had been established, the word came to take on a more of an ironic tone with the writers and poets of the time, as they began using it to describe the urban, pleasure quarters in the great cities of the then-shogunate. It became especially popular when the ukiyo-e, pictures of the floating world, became popular among common and noble classes, alike. 
As not much has changed within the red-light districts over the intervening centuries, it is still most often used as a general parlance for the districts of any city which house the pleasure houses, drinking dens, and gambling establishments, along with Hanamachi, Yukaku, and Hongdengqu, which are the official names for such districts.