Bastille Day is the French national holiday celebrated every year on July 14th. When in France, you may call the holiday La Fête Nationale (National Celebration), or Le Quatorze Juillet (the fourteenth of July).
The holiday memorializes the 1790 Fête de la Fédération, a festive commemoration held on the first anniversary of the July 14th, 1789 storming of the Bastille fortress-prison.
The storming of the Bastille was an episode in French history where protesters demonstrated against the tyrannical royal authority and raided the Bastille for arms and ammunition. To the citizens, the prison was the ultimate symbol of royal oppression and autocracy. Prisoners included people jailed on flimsy, arbitrary royal indictments and political prisoners imprisoned for publishing material found offensive to the royal court.