A bar could refer to a business where alcohol, such as beer or wine (or synthehol or synthale) is served, or the distinctive raised counter typically found within on which drinks are served. The workers who staff the bar are called bartenders.
Ten-Forward had a bar, and Guinan was the bartender.
By 2294, retired Starfleet Captain Montgomery Scott was known to frequent a bar in Glasgow, Scotland, where he obtained alcohol to help control his grief and depression over the loss of his former commanding officer, James T. Kirk. One night while there, he had a chance encounter with Guinan, where they shared several rounds of Saurian brandy. This delayed him from leaving long enough that he met Matt Franklin, and the two shared further rounds in the bar in Franklin's hotel. (Star Trek novel: Engines of Destiny)