The length of time an item remains in your inventory if not destroyed by you or sold (if possible). After this time, the item destroys itself. Different from the standard buff, debuff, or spell duration. A duration may be given as a span of real time, in which case the item disappears after that amount of time has passed in the real world (as opposed to in the game world). When items with a duration are stackable, units added to an existing stack will obtain the duration of that stack. Thus the timespan of items can be extended so long as items of a newer duration can be obtained.