Meltdown is an enemy skill that deals damage equal to the user's current HP to the entire party, but kills the user. It is used by powerful bosses including Omega and Armstrong. The Complete Collection adds in the Death Machine in Golbez's Challenge Dungeon, who can also use Meltdown.
Meltdown is an enemy ability used by the Doll family of monsters. It deals Fire damage to all characters in a circular area centered on the Doll itself.
Self-KO. Deals area damage equal to own HP.
Melting is a physical process that results in the phase transition of a substance from a solid to a liquid. Nuclear meltdown is an informal term for a severe nuclear reactor accident that results in core damage from overheating.