According to J.R.R. Tolkien via wikipedia http://en.wikipedia.org/wiki/Troll_(Middle-earth) Stone-trolls were Trolls who turned into stone during daylight, like the Trolls in The Hobbit. They could speak, and used a debased form of Westron (rendered into Cockney English in The Hobbit). Hill-trolls are described as having killed Arador, Chieftain of the Rangers of the North and grandfather to Aragorn. Tolkien described the trolls of that region, including the three from The Hobbit, as stone-trolls, suggesting that hill-trolls might be a sub-class or alternate term for such. However, the Army of the West fought "hill-trolls" of Gorgoroth that could move in sunlight at the Black Gate, inferring that these hill-trolls, at least, were Olog-hai rather than stone-trolls. Cave-trolls were seen in Moria. One was described as having dark greenish scales and black blood. Their hide was thick enough that when Boromir struck one in the arm his sword was notched and did no damage. However, Frodo Baggins was able to impale the "toeless" foot of the same troll with the enchanted dagger Sting. Mountain-trolls were mentioned once, wielding the great battering ram Grond in shattering the gates of Minas Tirith. From their name they are generally assumed to live in the mountains, and their choice as the creatures to wield Grond is sometimes taken to suggest that they were particularly strong even for trolls. Snow-trolls are mentioned only to describe Helm Hammerhand. When Helm went out clad in white during the Long Winter to stalk and slay his enemies, he was described as looking like a snow-troll. It thus seems implied that these trolls were white in colour and lived in cold climates, but otherwise nothing is known of them. Olog-hai were "strong, agile, fierce, and cunning" trolls created by Sauron, not unlike the Uruk-hai, and were able to withstand sunlight while under the sway of Sauron's will. They seldom spoke and were said to know no language other than the Black Speech, in which Olog-hai means "troll-folk" (singular Olog "troll"). Because of their cunning, they were thought by some to be giant Orcs, rather than trolls. They appeared towards the end of the Third Age and could be found near Dol Guldur and in the mountains around Mordor. In the Battle of the Morannon, there appear "hill-trolls" of Gorgoroth which are implied to be Olog-hai in one of the Appendices to The Lord of the Rings (the term is not used within the story proper). These were described as being taller and wider than men, and their hide or armour was described as a mesh of horny scales. They had black blood. Peregrin Took slew the leader of these trolls at the Battle of the Morannon; and after the destruction of the One Ring and the fall of Sauron, the surviving trolls scattered as if mindless.