Letter of marque
A letter of marque is a letter from a government allowing a captain and/or ship to commit warfare to ships of the enemy of the state. It is a license legalizing piracy. It allowed privateers to attack other ships to take their cargo and/or their ship.
Letters of marque were not only issued during wartime but also outside of it, as a form of economic warfare. Just so that the country would gain an advantage in the world trade over another country. It was a very cheap form of war for a government as potential privateers were a lot of times expected to pay for the license. And there would be no cost at all for the country's own navy.
The letter would contain all the details of the privateer (the captain) which ships of which nation he was allowed to attack, in which area he could operate, from which date to date the letter was valid, if and how he was expected to return the ships he conquered to the country that issued the letter, and it would contain an agreement on how to divide the price money.
In the past it had happened that a single person gained letters of marque from more than one government, cheating the system. This practise not to be confused with flying a False flag which was a legal warfare tactic, bound by specific rules.
In the same fashion as with pirates the crew isn't awarded a salary but get shares of the loot, this led to unrest when a privateer could not find a suitable ship to attack, and they may be tempted to find the borders of their license and resort to piracy.
Any ship and cargo they gained had to be brought back to the country of the issuer of the letter. There, the government would take a sizeable share. As high as 90% of the value of ship and cargo, the rest was for the privateers.
Letter of marque for captain R.A. Oak
After the Battle at Klein Curaçao in the ABC War where the sailing vessel Sunset Dawn saved the Zr.Ms. Willem Barentsz by attacking and sinking the Almirante General. Captain R.A. Oak received a letter of marque from the King of the Netherlands, which worked retroactively to cover the events of the ABC war.
Subsequently all crew members were offered a blanket pardon for their pirate actions in the time before the ABC war, if they would supply the Dutch government their names and details. The pardon did not cover any other crimes. Unsurprisingly not a whole lot of crew members were interested in that, as they knew the governments of the world didn't know who they were, and they liked to keep it that way, also some of them had a history they didn't want catching up with them. In the end only Rose, Bobby and Alejandro got the pardon.
Pirate or Privateer
A privateer is a crew member of a ship sailing with a letter of marque. They are licensed by a state to attack and take over ships of the enemy of the state. By using their own ship. Simply said it is a licensed pirate who has to share the loot with the government.
A pirate is a crew member of a ship conducting in piracy, not bound by any nation's rules and laws, attacking and robbing ships of their own choice, keeping all the spoils themselves.
Also Privateers are the amazing followers of this World Anvil world.
Piet Hein is maybe the most famous Dutch privateer, Admiral in the WIC. In 1628-1629 he commanded a fleet of 31 ships and sailed for the Caribbean with the plan to attack and hijack the Spanish Treasure Fleet that sailed annually back to Spain.
He was successful, otherwise he wouldn't have been famous, and captured the entire fleet. With a value of 12 million Gulden (1628). This amount was so big for the time that it had a visible effect on the world economics. Spain suffered and the Republic of the Netherlands, suddenly had the money to fund sieges in the 80 year war against Spain.
The share holders of the WIC got that year a 50% dividend payout. The stock market value of the WIC rose by 225%. They rewarded the crew of the privateer fleet with 17 months of extra salary. Piet Hein himself 6.000 Gulden and the crew 200 Gulden each.