Bastille Day is the common name given in English-speaking countries/lands to the French National Holiday, which is celebrated on the 14th of July each year. In France, it is formally called la Fête nationale. The National Celebration.
The name “Bastille” comes from the word bastide, which means “fortification”; it was used as a generic term for a certain type of tower in Southern France until it was eventually restricted to one particular Bastille. When construction began on the building in 1357, its main purpose was not to keep prisoners in, but to keep invading armies out: At the time, France and England were engaged in the Hundred Years’ War. The Bastille—known formally as the Bastille Saint-Antoine—was conceived as a fortress whose strategic location could help stall an attack on Paris from the east.