Information that has been determined pursuant to Executive Order 12958 as amended by Executive Order 13292, or any predecessor order, or by the Atomic Energy Act of 1954, as amended, to require protection against unauthorized disclosure and is marked to indicate its classified status.
Sources:
NIST SP 800-18 Rev. 1
under National Security Information
NIST SP 800-60 Vol. 1 Rev. 1
under National Security Information
NIST SP 800-60 Vol. 2 Rev. 1
under National Security Information