In law, an absolute defence (or defense) is a factual circumstance or argument that, if proven, will end the litigation in favor of the defendant.
Another characteristic of an absolute defence is that, when it is pleaded and proven, it is not subject to mitigation or collateral attack.
Most notably, innocence, while a complete defense to a criminal charge, is not generally termed "absolute", because it involves a material fact of the pleading.
On the other hand, double jeopardy is more likely to be termed an absolute defence; an indictment or (other criminal initiating pleading) does not have to state that the defendant has not previously been tried on the crime, but once a defendant shows that he has been previously tried for a crime, his dismissal is required by the US Constitution.
Examples include diminished capacity to understand the wrongfulness of the action, or a mistake of fact that affected the intention of the litigant.