Reference states that during the U.S. prohibition, from 1920-1933, illegal bars were commonly called speakeasies. The term originated from how a customer ordered alcohol without raising suspicion. The bartender would instruct the customer to be quiet and speak easy.
Speakeasies proved to be lucrative businesses as prohibition progressed. They manufactured, sold and transported illegal alcohol.
Other slang terms for a speakeasy were blind pig, gin joint and gin mill. Typically, speakeasies were higher class and offered entertainment such as live bands or floor shows, music and food, in addition to alcohol. Blind pigs usually referred to a lower-class establishment offering only beer and other liquors.