In Internet slang, a troll (//, //) is someone who posts inflammatory, extraneous, or off-topic messages in an online community, such as a forum, chat room, or blog, with the primary intent of provoking readers into an emotional response or of otherwise disrupting normal on-topic discussion. The noun troll may also refer to the provocative message itself, as in: "That was an excellent troll you posted."
While the word troll and its associated verb trolling are associated with Internet discourse, media attention in recent years has made such labels subjective, with trolling describing intentionally provocative actions and harassment outside of an online context. For example, mass media has used troll to describe "a person who defaces Internet tribute sites with the aim of causing grief to families."
The most likely derivation of the word troll can be found in the phrase "trolling for newbies", popularized in the early 1990s in the Usenet group, alt.folklore.urban (AFU). Commonly, what is meant is a relatively gentle inside joke by veteran users, presenting questions or topics that had been so overdone that only a new user would respond to them earnestly. For example, a veteran of the group might make a post on the common misconception that glass flows over time. Long-time readers would both recognize the poster's name and know that the topic had been discussed a lot, but new subscribers to the group would not realize, and would thus respond. These types of trolls served as a practice to identify group insiders. This definition of trolling, considerably narrower than the modern understanding of the term, was considered a positive contribution. One of the most notorious AFU trollers, David Mikkelson, went on to create the urban folklore website Snopes.com.
By the late 1990s, alt.folklore.urban had such heavy traffic and participation that trolling of this sort was frowned upon. Others expanded the term to include the practice of playing a seriously misinformed or deluded user, even in newsgroups where one was not a regular; these were often attempts at humor rather than provocation. In such contexts, the noun troll usually referred to an act of trolling, rather than to the author.
Early incidents of trolling were considered to be the same as flaming, but this has changed with modern usage by the news media to refer to the creation of any content that targets another person. The Internet dictionary NetLingo suggests there are four grades of trolling: playtime trolling, tactical trolling, strategic trolling, and domination trolling. The relationship between trolling and flaming was observed in open-access forums in California, on a series of modem-linked computers in the 1970s, like CommuniTree which when accessed by high school teenagers became a ground for trashing and abuse. Some psychologists have suggested that flaming would be caused by deindividuation or decreased self-evaluation: the anonymity of online postings would lead to disinhibition amongst individuals Others have suggested that although flaming and trolling is often unpleasant, it may be a form of normative behavior that expresses the social identity of a certain user group  According to Tom Postmes, a professor of social and organisational psychology at the universities of Exeter, England, and Groningen, The Netherlands, and the author of Individuality and the Group, who has studied online behavior for 20 years, "Trolls aspire to violence, to the level of trouble they can cause in an environment. They want it to kick off. They want to promote antipathetic emotions of disgust and outrage, which morbidly gives them a sense of pleasure."
In academic literature, the practice of trolling was first documented by Judith Donath (1999). Donath's paper outlines the ambiguity of identity in a disembodied "virtual community" such as Usenet: In the physical world there is an inherent unity to the self, for the body provides a compelling and convenient definition of identity. The norm is: one body, one identity ... The virtual world is different. It is composed of information rather than matter.Donath provides a concise overview of identity deception games which trade on the confusion between physical and epistemic community: Trolling is a game about identity deception, albeit one that is played without the consent of most of the players. The troll attempts to pass as a legitimate participant, sharing the group's common interests and concerns; the newsgroups members, if they are cognizant of trolls and other identity deceptions, attempt to both distinguish real from trolling postings, and upon judging a poster a troll, make the offending poster leave the group. Their success at the former depends on how well they – and the troll – understand identity cues; their success at the latter depends on whether the troll's enjoyment is sufficiently diminished or outweighed by the costs imposed by the group. Trolls can be costly in several ways. A troll can disrupt the discussion on a newsgroup, disseminate bad advice, and damage the feeling of trust in the newsgroup community. Furthermore, in a group that has become sensitized to trolling – where the rate of deception is high – many honestly naïve questions may be quickly rejected as trollings. This can be quite off-putting to the new user who upon venturing a first posting is immediately bombarded with angry accusations. Even if the accusation is unfounded, being branded a troll is quite damaging to one's online reputation.Susan Herring and colleagues in "Searching for Safety Online: Managing 'Trolling' in a Feminist Forum" point out the difficulty inherent in monitoring trolling and maintaining freedom of speech in online communities: "harassment often arises in spaces known for their freedom, lack of censure, and experimental nature". Free speech may lead to tolerance of trolling behavior, complicating the members' efforts to maintain an open, yet supportive discussion area, especially for sensitive topics such as race, gender, and sexuality.