Plate is warrior, paladin, and death-knight gear, and tanking plate with defensive stats holds a premium over same-level damage plate. Plate — one of the subtypes World of Warcraft files under Armor — gets this table as a focused view: the same drill-down the in-game Auction House browser applies when you filter by subcategory.
Plate listings clear and replenish at whatever pace the in-game market sets; some subtypes trade in volume, others sit static for stretches. The price-history chart on each row's detail page makes that pattern visible at a glance.
The "Browse subcategories" links on the parent Armor page list every other subtype if you want to compare markets side by side.