The subject of this article originates from non-canonical sources. To find out about what is considered "canon" see LOTR:Canon.
As discovered by Bilbo on his Quest to the Lonely Mountain, they are so sensitive to sunlight that they're instantly turned to stone if exposed to it. They are believed to be the most intelligent race of trolls to live, being the only breed capable of speech. In the Two Towers video game, five forest trolls are seen, though four are in daylight and are not turned to stone. Also many are seen in The Lord of the Rings: Aragorn's Quest, all in daylight and alive, exact the three Bilbo saw, as statues.
These trolls and the information are video game inventions and only appear in The Lord of the Rings: Aragorn's Quest.