Powers not delegated refers to the idea that any powers not specifically given to the federal government in the Constitution are reserved for the states or the people. In other words, if a power is not listed in the Constitution as belonging to the federal government, then it belongs to either the states or the people.
Related terms
Federalism: This term refers to a system of government where power is divided between a national/federal government and state governments.
Reserved powers: These are powers that are specifically set aside for either state governments or for individuals.
Tenth Amendment: The Tenth Amendment to the United States Constitution explicitly states that any powers not delegated to Congress nor prohibited by it are reserved for either individual states or for individual citizens.