Corsairs (French: corsaire) were privateers, authorised to conduct raids on shipping of a foreign state at war with France, on behalf of the French crown. Seized vessels and cargo were sold at auction, with the corsair captain entitled to a portion of the proceeds. Although not French Navy personnel, corsairs were considered legitimate combatants in France (and allied nations), provided the commanding officer of the vessel was in possession of a valid letter of marque (lettre de marque or lettre de course, the latter giving corsairs their name), and the officers and crew conducted themselves according to contemporary admiralty law. By acting on behalf of the French Crown, if captured by the enemy, they could in principle claim treatment as prisoners of war, instead of being considered pirates.
Because corsairs gained a swashbuckling reputation, the word "corsair" is also used generically as a more romantic or flamboyant way of referring to privateers, or even to pirates. The Barbary pirates of North Africa as well as the Ottoman Empire were sometimes called "Turkish corsairs".