Bastille is a French word meaning 'castle' or 'stronghold'. Used as a single word ("la Bastille" in French, "the Bastille" in English) it invariably refers to the Bastille Saint-Antoine in Paris.
Built around 1370 as part of the defences of Paris, the structure was converted into a prison in the 17th century, housing mainly political prisoners. Its storming, and subsequent demolition, in 1789 by a large crowd is the symbol for the beginning of the French Revolution.
On May 5, 1789, Louis XVI convened the Estates General to hear their grievances. The deputies of the Third Estate, representing the common people (the two other estates were clergy and nobility) decided to break away; they eventually declared themselves to be a "National Assembly". (See Glossary of the French Revolution.) On June 20, the deputies of the Third Estate took the Tennis Court Oath (named after the gathering place where an ancestor of tennis, Jeu de Paume was played), swearing not to separate until a constitution had been established.
On July 2nd, 1789, the Bastille prisoner Marquis de Sade reportedly shouted out of his cell to the crowd outside, "They are killing the prisoners here!", causing somewhat of a riot. He was immediately transferred to the insane asylum at Charenton. The confrontation between the commoners and the ancien régime ultimately led to the people of Paris storming the Bastille on July 14, 1789. At this point, only seven inmates were housed there.
Many historians believe that the storming of the Bastille was more important as a rallying point and symbolic act of rebellion than any practical act of defiance. No less important in the history of France, it was not the image typically conjured up of courageous French patriots storming the Bastille and freeing hundreds of oppressed peasants.
This event is commemorated on Bastille Day (Quatorze juillet), the French national holiday.
The former location of the fort is currently called the Place de la Bastille, and some of the remains (although not at their original location) are still visible nearby. The actual fort was demolished soon after its capture and the rubble sold as souvenirs and used for the Pont de la Concorde.