Alternatively, you might want to import some information from a database site - see: WowheadThottbotWoWDB for listings.
Thunderforged is a new sub-type of raid item drop quality introduced with Patch 5.2 in the Throne of Thunder raid similar to the Elite and Heroic Elite items. Each Patch 5.2 raid boss will have a chance of dropping this new designation of a particular item that's 6 item levels higher than their counterparts. Thunderforged items will drop more frequently in 25-player raids.Tier 15 armor pieces won't be available in Thunderforged quality at all.
There may actually be separate tiers for 10-man and 25-man like for Elite and Heroic Elite items, but that has not been announced so far.