Marque \Marque\, n. [F. marque, in lettre de marque letter of marque, a commission with which the commandant of every armed vessel was obliged to be provided, under penalty of being considered a pirate or corsair; marque here prob. meaning, border, boundary (the letter of marque being a permission to go beyond the border), and of German origin. See March border.]

(Law) A license to pass the limits of a jurisdiction, or boundary of a country, for the purpose of making reprisals.

Letters of marque, Letters of marque and reprisal, a license or extraordinary commission granted by a government to a private person to fit out a privateer or armed ship to cruise at sea and make prize of the enemy's ships and merchandise. The ship so commissioned is sometimes called a letter of marque.

Source: Webster's Revised Unabridged Dictionary (1913)