is a specific kind of: agency, authority, bureau, federal agency, government agency, office.

is a broader term that covers: AEC, Atomic Energy Commission | Manhattan Project | Council of Economic Advisors | National Security Council, NSC | Council on Environmental Policy | Joint Chiefs, Joint Chiefs of Staff | Office of Management and Budget, OMB | United States Trade Representative, US Trade Representative.

is a part of: executive branch, Executive Office of the President.