A more thorough explanation:

Collateral defense is a type of defense used in criminal law that does not directly challenge the prosecutor's allegations. Instead, it is a defense of justification or excuse that is collateral to the elements that the prosecutor must prove. For example, a defendant may argue that they committed a crime in self-defense, which is a collateral defense because it does not dispute the fact that they committed the crime, but rather justifies it.

Other examples of collateral defenses include the defense of habitation, which justifies the use of force to protect one's home, and the choice-of-evils defense, which argues that the defendant committed a crime to prevent a greater harm.

Collateral defenses are different from affirmative defenses, which are assertions of facts and arguments that, if true, will defeat the plaintiff's or prosecution's claim, even if all the allegations in the complaint are true. The burden of proof is on the defendant to prove an affirmative defense.

Overall, collateral defenses are used to justify or excuse a defendant's actions, rather than directly challenge the prosecutor's allegations.