A doctrine that federal powers should be curtailed and returned to the individual states WordNet 3.0 & Open English WordNet

In American political discourse, states' rights are political powers held for the state governments rather than the federal government according to the United States Constitution, reflecting especially the enumerated powers of Congress and the Tenth Amendment. Wikipedia

Political powers not expressly made over to the US federal government, and thus reserved for the states Wikidata

Rights reserved to the 50 United States which supposedly allow each one to set policy on some issues, rather than being subject to federal policy. Wiktionary