Code of Federal Regulations Title 40. Protection of Environment § 40.11.4 Definitions

(1) Top Secret. Top Secret refers to national security information or material which requires the highest degree of protection. The test for assigning Top Secret classification shall be whether its unauthorized disclosure could reasonably be expected to cause exceptionally grave damage to the national security. Examples of “exceptionally grave damage” include armed hostilities against the United States or its allies;  disruption of foreign relations vitally affecting the national security;  the compromise of vital national defense plans or complex cryptologic and communications intelligence systems;  the revelation of sensitive intelligence operations;  and the disclosure of scientific or technological developments vital to national security. This classification shall be used with the utmost restraint.

(2) Secret. Secret refers to that national security information or material which requires a substantial degree of protection. The test for assigning Secret classification shall be whether its unauthorized disclosure could reasonably be expected to cause serious damage to the national security. Examples of “serious damage” include disruption of foreign relations significantly affecting the national security;  significant impairment of a program or policy directly related to the national security;  revelation of significant military plans or intelligence operations;  and compromise of scientific or technological developments relating to national security. The classification Secret shall be sparingly used.

(3) Confidential. Confidential refers to that national security information or material which requires protection. The test for assigning Confidential classification shall be whether its unauthorized disclosure could reasonably be expected to cause damage to the national security.