A privateer was a private warship authorized by a country's government by letters of marque to attack foreign shipping. Strictly, a privateer was only entitled to attack enemy vessels during wartime. However, states often encouraged attacks on opposing powers while at peace, or on neutral vessels during time of war, blurring the line between privateering and piracy.
Privateers were an accepted part of naval warfare from the 16th to the 19th centuries, authorised by all significant naval powers. The costs of commissioning privateers was borne by investors hoping to gain a significant return from prize money earned from enemy merchants.