A more thorough explanation:

The insanity defense is a legal defense that a defendant can use in a criminal trial. It means that the defendant admits to committing the crime but argues that they are not responsible for their actions because of a mental illness.

For example, if someone with schizophrenia commits a crime, they may use the insanity defense to argue that they were not in control of their actions because of their mental illness.

The insanity defense is different from the diminished capacity defense, which is used to argue that the defendant did not have the intent to commit the crime because of a mental disorder.

There are different tests used to determine if someone is legally insane, including the M'Naghten rule, the irresistible impulse test, and the Durham rule. The Model Penal Code is a more modern approach to the insanity defense that combines cognitive and volitional components.

The insanity defense is controversial and has been criticized for being overused and difficult to prove. Some people argue that it should be abolished altogether.