Most people mean powers of government not specifically delegated to the federal government when they talk about "states rights".
I think speaking of any branch of Gov't as having 'rights'confuses the reason why we have gov't.
The States have their areas of responsiblities and power as does the Federal gov't.
Neither have 'rights'.
This is what caused so much confusion before the Civil War.
This was Calhoun's notion that the State was itself a sovereign entity and had 'rights'to protect when it was, in fact, a part of the Federal system whose function was to protect individual rights.
Most people mean powers of government not specifically delegated to the federal government when they talk about "states rights".
Conveniently [there's that word again] ignoring that States are prohibited by the Constitution from infringing upon individual rights.