Definition of magna cartas:
(n) :
(historical) A charter granted by King John to the barons at Runnymede in 1215, which is one of the bases of English constitutional tradition; a physical copy of this charter, or a later version.
(n) :
(law) A modified version of the charter of King John as granted by Henry III in 1236, confirmed as a statute by the Parliament of King Edward I in 1297, part of which remains in force in England and Wales.
(n) :
(figuratively) A landmark document that sets out rights or important principles.