Yes, a Q is a DOE term. I believe that today the term is somewhat used synonymously with TS/SCI clearances - because both clearances involve the same level. A Q or a TS/SCI require the highest possible FBI and other background checks.
I had a TS/SCI. We called it that, not Q. But the term "Q Clearance" is probably used interchangeable with TS/SCI in some government circles today.
Thanks. I didn't know