Speakeasy
The term speakeasy comes from the time of Prohibition. From 1920 to 1933, alcohol was banned by law throughout the USA; as a result, numerous clandestine speakeasies sprang up across the country. The name 'speakeasy' stems from the fact that people were supposed to speak as quietly as possible in the hidden bars so as not to attract attention.
At the time of Prohibition people often resorted to illegaly distilled spirits (quite a few speakeasies were run by members of organized crime), the speakeasies also had a significant influence on the cocktail recipes of their time; these were less 'classic' and more designed to mask the taste of the often inferior alcohol.
Nowadays, the term speakeasy is making a comeback and you increasingly hear about exclusive clubs that attract attention by word of mouth and, for example, can only be entered by reciting a certain password.