Retroactivity
Retroactivity refers to the application of a law or judicial decision to events that occurred before the law was enacted or the decision was made. In this case, it addresses whether the invalidation of a tax scheme affects taxes assessed before the ruling.
Dormant Commerce Clause
A legal doctrine derived from the Commerce Clause in the U.S. Constitution, which prohibits states from passing legislation that discriminates against or excessively burdens interstate commerce, even in the absence of federal legislation regulating the matter.
Internal Consistency Test
This test assesses whether a state's tax scheme is internally consistent in treating similar entities or transactions uniformly. If a tax discriminates against interstate commerce in its structure, it may fail this test.
Facially Discriminatory Tax
A tax that, on its face, appears to treat different entities or transactions unequally without a legitimate state interest. Such taxes are often scrutinized under the Dormant Commerce Clause for potential discrimination against interstate commerce.