term:

Imperfect Self-Defense

imperfect self-defense n

: a defense based on self-defense that does not shield the defendant from all liability but reduces the liability esp. because the defendant actually but unreasonably believed that he or she was in imminent danger of death or great bodily injury NOTE: Imperfect self-defense is not recognized in all jurisdictions. When it is successfully used in criminal cases it eliminates the element of malice, reducing the level of the offense from murder to manslaughter.

Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.