A State Paper is a document or file kept by a government to record discussions, options and decisions by government officials, departments and civil servants. Some states follow a thirty year rule whereby state papers on an issue may be released to academic scrutiny thirty years after an original discussion or decision.
State papers are often kept in a country's National Archives, State Paper Office or Public Record Office. All files are numbered using an alphanumeric code which academics may use as a reference in footnotes of books.
Some state papers are embargoed for reasons of national security or other sensitive reasons.
References
State paper Wikipedia(Text) CC BY-SA