Captain was a nautical term and the traditional title given to a person in charge of a ship at sea. Legal documents often correctly refer to these people as the ship's master. The word came to English via French from the Latin "capitaneus" ("chief") which is itself derived from the Latin word "caput" ("head"). The analogous French title is Capitaine, which was notably used by the Pirate Lord Chevalle. The "Captain" is usually helped by the first mate, or bo'sun.
Some captains, like Jack Sparrow, owned their ships, while others such as James Norrington, commanded ships for others. The captain was the one to give the order to abandon ship. Disobeying the captain could be considered mutiny.