an archival document
a document that records the legal rights or privileges of a person, group, or organization
Muniments, in the second defintion, are kept for use as evidence to defend title or other property rights to land, possessions, or inheritances. In some, but not all, of these cases, “muniment” identifies a record created by a government or other organization in the conduct of its official business—as opposed to a “manuscript” collected by an archives. The first sense, nearly synonymous with “document,” is the most common one. The term is rarely used in the archival literature today, and it was and is much more commonly used in the British Empire than the United States.