What term describes information whose unauthorized disclosure could significantly harm national security?

The term that best describes information whose unauthorized disclosure could significantly harm national security is classified as 'Top Secret.' This level of classification is reserved for information that, if disclosed, could cause "exceptionally grave damage" to national security.

While options such as "Confidential" and "Secret Classification" indicate various levels of sensitive information, they do not convey the highest potential risk associated with disclosure. "Confidential" refers to information that could cause damage to national security if revealed, but it does not reach the severity described by 'Top Secret.' Alternatively, 'Secret Classification' pertains to information requiring protection because its disclosure could cause serious damage but is still not of the utmost sensitivity associated with 'Top Secret.'

On the other hand, 'Restricted Access' is a more general term and does not specifically correlate with the established classification levels used in national security contexts. Thus, the most appropriate term to indicate that the unauthorized disclosure of such information could significantly harm national security is 'Top Secret.'