How secret is top secret?

From the Winter 2007 issue of The News Media & The Law, page 33.

On March 28, 2003, President George W. Bush signed an executive order that amended previous rules on the procedure for classifying information. In addition to designating who may properly classify information, and how long the information may remain protected, the order describes what each of the three classification levels mean:

Top Secret: “Applied to information, the unauthorized disclosure of which reasonably could be expected to cause exceptionally grave damage to the national security that the original classification authority is able to identify or describe.”

Secret: “Applied to information, the unauthorized disclosure of which reasonably could be expected to cause serious damage to the national security that the original classification authority is able to identify or describe.”

Confidential: “Applied to information, the unauthorized disclosure of which reasonably could be expected to cause damage to the national security that the original classification authority is able to identify or describe.”

Short of formal classification, the government can also block the release of information if Congress grants it the proper authority. The Transportation Security Administration, for example, can block release of various airport screening techniques it deems to be “sensitive security information.” This type of so-called “sensitive but unclassified” information comes in many different forms depending on the agency and critics say it is wildly overused.

Source: Executive order 13292, “Classified National Security Information, as amended,” § 1.2 “Classification Levels”