A type of ranged weapon that usually causes only physical damage and doesn't need ammo to use, instead the weapon loses 1 out of 200 durability per throw, and requires a repair once it reaches 0 durability.
All Rogues start with the throw ability, and later gain the ability Deadly Throw, which requires a thrown weapon to be equipped. Hunters and Warriors can learn the throw skill from some trainers (see weapon trainers for details), though 'throwing' differs from 'shooting'; hunters in particular, have little use for them given their shooting-weapon oriented skills. By contrast, Warriors and rogues prefer throwing weapons for itemization simplicity (i.e., 'ammo' that is a single item which lasts quite a while), and primarily use them to pull specific mobs.
Drysc: "The mechanic of thrown weapons is being changed in the expansion to be similar to a normal weapon. Once a stack is used it will remain in your inventory and can then be repaired to refill the stack, similar to repairing broken armor or weapons. This allows us to put stats on thrown weapons and itemize them as we would any other weapon." 
Some examples : http://www.thottbot.net/beta?iclass=2.16
There is a bug currently in game that still causes throwing weapons to be used up even though the patch was implemented to stop this. Blizzard claims they are working on a fix for this bug.