Blind pig

Blind pig is a term sometimes used for an illegal drinking place. This term was the most popular during the Prohibition Era (1920-33), when alcohol was illegal in the U.S. Cases such as this one from Michigan explain that “blind pig” was a commonly used term during the Prohibition Era for a “speakeasy,” a place that sells alcoholic beverages illegally.

It is often used synonymously with “blind tiger”. 

See: blind tiger