The difference between a bar and a tavern varies, depending on the region of the world where one is. In some areas, the two terms are used interchangeably, while in other places, people mean something very specific. Some regions distinguish between the two when it comes to licensing, making the difference primarily legal in nature.
Both facilities are established for the purpose of selling alcoholic beverages, typically for on sale use only, meaning that people cannot buy alcohol to take away. The beverages on offer vary, but typically include beer, hard liquor, various mixed drinks, and wine. Most bars and taverns have a literal bar, as in a counter where people can sit and socialize while drinking. The bar is used also as a staging point for mixing drinks, interacting with customers, and storing various equipment such as cups, garnishes, and so forth.
When people do distinguish between a bar and a tavern, they usually think of a bar as an establishment where only alcohol is available, while a tavern offers food as well as alcohol. In the legal sense, people below the legal drinking age may be allowed into a tavern, under the assumption that the facility acts as a restaurant, and therefore non-drinkers would have a legitimate reason to patronize it, whereas bars might be strictly off-limits to underage individuals. These facilities may also be given different licensing permits in terms of the hours of legal operation, the ability to provide live entertainment, and so forth.
Bars tend to be more likely to offer live entertainment like bands, strippers, magic acts, and so forth, and they may include things like jukeboxes, pool tables, and other forms of entertainment. The bar environment is very much geared to socialization and entertainment, with small tables which encourage people to crowd together, ample stools at the bar, and a relaxed atmosphere. Taverns, on the other hand, may be designed more for dining, with larger tables which can accommodate dinner or lunch service.