A troll rating on Daily Kos is a post or user whose posts have been rated as not useful by other users. The term "troll" is highly loaded and in general should be avoided in referring to persons. See this article for a broad discussion of the history and context of this term and why it is not neutrally applicable and is thus often abused in power structures.
In conjunction with the term:trusted user, the implication is that so-called "trolls" are "not trusted" by reasonable users, meaning, the existing users who rate posts. This implication is also questionable.