Congressional documents originate from congressional committees and cover a wide variety of topics and may include reports of executive departments and independent organizations, reports of special investigations made for Congress, and annual reports of non-governmental organizations. Congressional documents, along with Congressional reports, are part of the U.S. Congressional Serial Set, commonly referred to as the Serial Set.
Text source: FDsys
Image source: The Library of Congress
Proceeded by American State Papers, SuDoc# Y 1.1/2: