What is Moderata Misericordia?

Legal Definition
A writ founded on Magna Charta, which lies for him who is amerced in a court, not of record, for any transgression beyond the quality or quantity of the offence. It is addressed to the lord of the court or his bailiff, commanding him to take a moderate amerciament of the parties. New Nat. Brev. 167; Fitzh. Nat Brev. 76.
-- Black's Law Dictionary
Legal Definition
A writ to prevent excessive amercement.
-- Ballentine's Law Dictionary