Reduces the chance melee attacks will hit you by X%.
Frigid Dreadplate is a Death knight talent located in the 5th tier of the Frost Tree. It reduces the chance enemies have to hit you in melee by up to 3%. While of some use in player versus player combat and solo play, it is primarily a tanking talent. For a tank, the relative value of the talent increases as your gear improves and your avoidance increases, but it should always be included in any tanking build. Together with Improved Frost Presence, it is one of the reasons why frost tanks generally take somewhat less damage than other death knight tanks.
Patch 3.0.8 (2009-01-20): Changed from "Enemies who hit you in melee have a 5/10/15% chance to become unsettled, decreasing their chance to hit you in melee by 50%." to "Reduces the chance melee attacks will hit you by 1/2/3%."