A more thorough explanation:

A collateral attack, also known as an indirect attack, is a legal challenge to the validity of a previous court decision through a new case instead of a direct appeal. This means that a party is trying to prove that a previous judgment was invalid by bringing up new evidence or arguments in a different case.

For example, a person who has been convicted of a crime might file a habeas corpus petition to challenge the validity of their conviction. This is a type of collateral attack because they are not appealing the conviction directly, but rather bringing up new evidence or arguments in a separate case.

Another example of a collateral attack is when a party claims that a previous judgment was invalid after the opposing party cites it for strategic advantage in a new case. This means that the party is trying to show that the previous judgment was not valid and should not be used against them in the new case.

Collateral attacks are often used when a party is barred from raising an issue or claim again because it has already been litigated on the merits. In these cases, the party must show that the initial judgment was invalid in order to re-litigate the issue or claim.

Common grounds for a collateral attack include a lack of personal jurisdiction, a lack of subject matter jurisdiction, and a failure of due process in the first case. For example, if a court did not have the authority to hear a case because the defendant did not live in the state, a collateral attack could be used to challenge the validity of the judgment.

Overall, a collateral attack is a way for a party to challenge the validity of a previous court decision through a new case. This can be done for a variety of reasons, such as to prove that the previous judgment was invalid or to raise new evidence or arguments that were not considered in the previous case.