Red Plate (also known as Red Mail in the SNES/PS version) is armor in Chrono Trigger and Chrono Cross. Effects vary between games.
Chrono Trigger
Absorbing all Fire Element damage and converting it into Hit Points, anyone in the party can wear it. It has a base defense of 70 and can be sold for 4100 G. To obtain, use Ayla's charm tech on the Rust Tyranno in the Giant's Claw or open the Sealed Chest in Guardia Castle, once the Pendant is charged by Mammon Machine.
Chrono Cross
Absorbing Red Elements and increasing weakness to Blue Elements, this armor can be worn by any character. It increase Defense +7, Magic Defense +4, and Evade% -3. To obtain, steal it from the second form of the Fire Dragon. It can be sold for 3962G.