Attack on a prior judgment in a new case (i.e., not by direct appeal). Also called an indirect attack. Examples include habeas corpus petitions and claims that a prior judgment was invalid after the opposing party cites it for strategic advantage in a new case.
For a habeas corpus case, see Miller-El v. Dretke 545 U.S. 231 (2005).
For how prior judgments can affect a new case, see res judicata and collateral estoppel.