Answer:
The idea that a state could refuse to follow a federal law it disagreed with
Explanation:
Nullification is the theory that states could refuse to follow federal laws that they disagreed with.
One example of this is the Nullification Crisis between South Carolina and the US government, over the Tariff of 1828, also called the Tariff of Abominations.
The state, under leadership of John C Calhoun, tried to nullify the tariff because it would hurt the Southern economy.