In the new expansion, Legion, item drops from Dungeons, World Quests and other content can come with extra item-levels, making the item stronger, but sometimes the item says Titanforged, and others, Warforged. What's the difference between them, and why they have different names for similar (if not the same) effect?
It's the very the same effect.
It only gets a different name once its upgrade value exceeds 10 item levels. Blizzard thought it looked cooler this way. 50 ilvl of Warforged items look and sound boring. Also you now see on the first glimpse, if you got something good or maybe something really cool.
Unlike previous Warforged items from WoD you now get a dice roll for every 5 iLvls added. So you need to be lucky four times in order to get something +20. In WoD it was one and done.
Also there is a cap: before the first raid starts next week the maximum you can get is 850. After that you can get items up to 895 (Legendary and Titanforged alike), probably increasing with every raid tier.
(Bluepost explaining the situation)