Maritime piracy, according to the United Nations Convention on the Law of the Sea (UNCLOS) of 1982, consists of any criminal acts of violence, detention, or depredation committed for private ends by the crew or the passengers of a private ship or aircraft that is directed on the high seas against another ship, aircraft, or against persons or property on board a ship or aircraft. Piracy can also be committed against a ship, aircraft, persons, or property in a place outside the jurisdiction of any state.

The English "pirate" is derived from the Latin term pirata and that from Greek peirates "brigand", ultimately from peira "attempt, experience", implicitly "to find luck on the sea". The word is also cognate to peril. In 17th and 18th century sources the word is often rendered "pyrate". However, the term does not exclusively relate to robbery committed at sea, as other similar origins have a broader definition.