Attuned

You can attune an item at a Stone of Change. All items that can be equipped (except quivers) can be placed into a Stone of Change with a number of Khyber Dragonshard Fragments to bind the item and prepare it for the later addition of Eldritch Rituals. An unbound item becomes bound to character, whereas an item already bound to account remains bound to account.

Binding and attuning an item used to require (minimum level of item ^ 2) Khyber Dragonshard Fragments, so a minimum level 12 item would require 144 fragments. As of Apr. 14, 2012 level 8, level 9, and level 11 items (at least) require 400 fragments. An item that is bound no longer takes permanent item damage when repaired, but permanent damage sustained up to that point cannot be repaired and the item can no longer be traded.

Note that there is a for items without a minimum level (i.e. minimum level 1) which makes them require 400 fragments instead of 1.