[Cboldt]

From what I understand, "Classified" is a generic umbrella term that includes "Confidential", "Secret", "Top Secret" and another level of codeword only access.

https://en.wikipedia.org/wiki/Classified_information_in_the_United_States

[lepton]

“Classified is a yes/no thing. Confidential, Secret, Top Secret (and it’s more narrow descriptors) are the level of classification.

While ‘Need to know’ applies in general, it is more sharply defined/limited amongst the subcategories of TS, where only some narrow group of people with TS clearances are allowed to know the information - it’s compartmentalized - and approval is document (or less) by document for a given individual. For example, the Sec of State may be allowed detailed knowledge of the content of a meeting with an informant, but be denied the details of the technology that collected it, or even the informants actual name, title, or physical description.