32 C.F.R. § 2400.6 – Classification levels.

(a) National security information (hereinafter “classified information”) shall be classified at one of the following three levels:
1. (1) “Top Secret” shall be applied to information, the unauthorized disclosure of which reasonably could be expected to cause exceptionally grave damage to the national security.
2. (2) “Secret” shall be applied to information, the unauthorized disclosure of which reasonably could be expected to cause serious damage to the national security.
3. (3) “Confidential” shall be applied to information, the unauthorized disclosure of which reasonably could be expected to cause damage to the national security.
(b) Except as otherwise provided by statute, no other terms shall be used to identify classified information. Markings other than “Top Secret,” “Secret,” and “Confidential,” such as “For Official Use Only,” shall not be used to identify national security information. In addition, no other term or phrase shall be used in conjunction with one of the three authorized classification levels, such as “Secret Sensitive” or “Agency Confidential.” The terms “Top Secret”, “Secret”, and “Confidential” should not be used to identify nonclassified executive branch information.
(c) Unnecessary classification, and classification at a level higher than is necessary shall be scrupulously avoided.
(d) If there is reasonable doubt about the need to classify information, it shall be safeguarded as if it were classified “Confidential” pending a determination by an original classification authority, who shall make this determination within thirty (30) days. If there is reasonable doubt about the appropriate level of classification the originator of the information shall safeguard it at the higher level of classification pending a determination by an original classification authority, who shall make this determination within thirty (30) days. Upon the determination of a need for classification and/or the proper classification level, the information that is classified shall be marked as provided in § 2400.12 of this part.