Re: "Secret" == "Not very import, interesting, or secret at all"
Far too often, secret is abused and things that should be unclassified are marked secret. Confidential is largely ignored.
The stupidest thing I ever saw was a group of DoD contractors, who were marking U/FOUO information as S/FOUO. Whiskey, Tango, Foxtrot, over?! FOUO is for unclassified information that should still remain free of FOI requests.
Of course, there's a full alphabet soup after the primary security level is determined, NOFORN being the least and I'll not bother getting into bigot lists.
But, I also started out in things nuclear, holding an N clearance and a standard clearance.
Top Secret is determined by whether the information being released would result in critical damage to the government.
Secret is determined whether the information being released would result in significant damage to the government.
Confidential is determined whether the information being released would result in minor damage to the government.
The damage could be to reputation, standing or things like everyone knowing precisely what is inside of the physics package on a modern thermonuclear warhead.
Unclassified is a valid security designated, if sensitive, such as personnel PII, it's designed Unclassified/FOUO (For Official Use Only) and is typically exempt from FOI requests (or the sensitive details removed from the document).
An N clearance is for things nuclear, in nuclear weapons fields, where direct access to the device is part of one's duties.
A Q clearance allows one just to be around a nuclear weapon, but not to directly access, handle or touch a device.
A Yankee White clearance allows one to be physically around the POTUS, such as workers in the White House and other locations the POTUS frequents.
I'm sure I missed a couple of oddball clearances, but it is late here.