Anonymity is the condition of being unknown, without a name or lacking an identity. The term is derived from the Greek word ανωνυμία, meaning "without a name" or "namelessness". This may also be termed facelessness, or lacking a public face, in the special sense of an evident appearance or identity.
Anonymity is a common characteristic of people in public places (such as sidewalks, crowds or shopping malls) and of cash-based market transactions. Anonymity is also closely related to certain aspects of the problem of privacy. In some respects, anonymity is the antithesis of community - in small, traditional, and closely-knit communities no one is anonymous and everyone has a recognizable name, face and identity.
Another aspect of anonymity is the use of pseudonyms. Many writers use a nom de plume; names like Voltaire and Mark Twain are much better known than the writers' real names. It is also common for actors or other performers to use a stage name. Several people might share a pseudonym, as for the mathematician Nicolas Bourbaki who published a number of papers and nine books but never actually existed or "Publius", the pseudonym three authors (Alexander Hamilton, James Madison and John Jay) used jointly for the Federalist Papers. Pseudonyms do not necessarily confer anonymity — it was well known that Mark Twain was actually Samuel Clemens, for example — but sometimes they allow the user to be effectively anonymous.
For a long time, courts tried to use dress to make the judges and lawyers appearing in court seem anonymous, to prevent threats from criminals and others in revenge for guilty verdicts. In recent years, court dress has been relaxed, but the importance of anonymity in the courtroom has shifted to victims and witnesses, especially in sexual abuse, rape and child abuse cases. To protect from the emotional distress of seeing the perpetrator, victims of rape and sexual abuse often give evidence behind a screen. Children often give testimony through a video link with the court, and some court sessions now let anonymous witness testimony be presented when it is deemed suitable. This is not without controversy: it is an important legal principle that one should be able to face one's accusers. There is considerable debate of how to weigh up the interests of justice in these cases with the needs and protection of victims and witness.
The topic of anonymity is a particular interesting and dynamic one in online contexts, especially in the broad set of media, software, websites, and venues identified as Web 2.0. Particularly when encountering existing or created web pages, the anonymous reader, known only to herself, frequently encounters an equally anonymous author.
Online anonymity is sometimes considered a vexing problem: to some, every anonymous participant online is a potential troll, terrorist, extortionist, pedophile or other criminal or anti-social being, while others seek in anonymity the protection of their privacy, and support for freer expression. The moderate middle balancing anonymity with responsibility for one's online actions, while desirable, has yet to be fully realized in a large number of online instances. Some communities require that members use their real names: pioneering forum community The Well is one example, as is the Citizendium. In other communities, like Anonymous and 4chan, anonymity is expected - either through posting without a username, posting as 'Anonymous' or using a throw-away pseudonym - using a real name in some communities is an invitation for harassment. Communities online that practice illegal activities often use pseudonyms or anonymity to protect the users from the legal consequences of their actions.
Pseudonyms, or fabricated names, whether or not the fabrication is obvious, are a common online phenomenon. Sometimes mnemonic devices may be used, whether or not they have meaning to the creator. Thus Betty Rice, who only a few close friends know plays in a bell choir, for example, may seek to retain her online anonymity with the pseudonym Bell Ringer.
The condition of being anonymous seldom appears among lists of key concepts in social science theories but is nonetheless related in complex ways to several important social and political ideas: It shares a first syllable (and common Greek origin) with anomie, for example, and is theoretically related as well to anarchy; the concern being that persons nameless or unknown may constitute threats to social order or moral order. The condition of anonymity is also closely linked to the social psychological concept of personal identity.
In politics and community theory, the concept of anonymity is often linked with the idea of membership: the outside is a stranger, an unknown person without a name or an identity, not one of us, not a member of our community. Robert and Sara Morris, in a book subtitled Why Care for the Stranger? argued that this is a concept with particularly important consequences in social welfare policy.  The poor and certain other disadvantaged populations who are the traditional subjects of welfare policy, they suggest, have long been largely anonymous - 'not one of us' - and hence, not really part of the community.
Some important political works have been published anonymously or under a pseudonym; the Federalist Papers are perhaps the best-known example.
Anonymity can also have positive political uses. Many nations, for example, pay tribute to all fallen heroes in monuments like the Tomb of the Unknown Soldier in Washington DC in which an anonymous corpse of a soldier from an unidentified war is buried.
Philosophically, important issues revolve around the question of the nature of existence of that which lacks a name or is fully unknown.
Although a significant body of anonymously written texts exist from antiquity and prior, texts are generally not attributed as properly written anonymously until after the scientific revolution, when authorship became an occasion for boasting.
- Morris, R., & Morris, S. M. (1986). Rethinking social welfare : why care for the stranger. New York, N.Y.: Longman.
- Agassi, Joseph. "Robert Boyle's Anonymous Writings". Isis, 1977, 68 (No. 242) Pp. 284 – 87. Available online.