How information gets classified.

From GovITwiki

The US Government has a uniform system for classifying, declassifying, and safeguarding national security information, according to the CIA.

CourtyardCONFIDENTIAL refers to national security information that requires protection. Its unauthorized disclosure could reasonably be expected to cause damage to national security.

SECRET refers to national security information that requires a substantial degree of protection. Unauthorized disclosure could reasonably be expected to cause serious damage to national security.

TOP SECRET refers to national security information that requires the highest degree of protection.

Unauthorized disclosure could reasonably be expected to cause exceptionally grave damage to national security. By law and regulations, much intelligence information automatically becomes declassified after a specific period of time. Exemptions are provided for certain types of sensitive information.