A tavern is a place of business where people gather to drink alcoholic beverages and be served food, and (historically) where travelers would receive lodging. An inn is a tavern that has a license to put up guests as lodgers. The word derives from the Latin taberna whose original meaning was a shed, workshop, stall, or pub.
Over time, the words "tavern" and "inn" became interchangeable and synonymous. In England, inns started to be referred to as public houses or pubs and the term became standard for all drinking houses.