Final answer:
During the Prohibition era, underground saloons known as 'speakeasies' served alcohol illegally. They required a password or invitation for entry and were often operated by organized crime groups.
Step-by-step explanation:
During the Prohibition era in the United States, underground saloons where alcohol was illegally served were known as 'speakeasies.' These clandestine establishments were hidden from public view and required a secret password or invitation for entry. They became popular venues for socializing and drinking during a time when alcohol was banned, and they were often run by organized crime groups. The operation of speakeasies contributed to the rise of bootlegging and the illegal distribution of alcohol.