A pseudonym, (from the Greek ψευδώνυμον /psev΄donimon/), (often abbreviated pseud. when used in book publishing) is a fictitious alternative to a person's legal name. In some cases, pseudonyms are adopted because it is part of a cultural or organizational tradition, as in the case of devotional names used by members of some religious orders and "cadre names" used by Communist party leaders such as Trotsky and Stalin.

Pseudonyms are also used to hide an individual's identity, as with writers' pen names, graffiti artists, resistance fighters or terrorists' noms de guerre and computer hackers' handles. An example is of the well known fictional spy character James Bond concealing his identity by using the pseudonym "James St. John Smith" in the film A View To A Kill. Actors, musicians, and other performers sometimes use stage names, for example to mask their ethnic backgrounds. Stage names are also used to create a name which better matches their stage persona, as in the case of hip hop artists such as Ol' Dirty Bastard (who was known under at least six aliases); Black metal performers such as Nocturno Culto; and hardcore punk singers such as "Rat" of Discharge.

A collective name or collective pseudonym is one shared by two or more persons. This is sometimes used by the co-authors of a work, such as Ellery Queen.

The term is derived from the Greek lang: ψευδώνυμον (pseudṓnymon), literally "false name", from (pseûdos), "lie, falsehood" and (ónoma), "name". A pseudonym is distinct from an allonym, which is the name of another actual person, assumed by someone in authorship of a work of art; such as when ghostwriting a book or play, or in parody, or when using a "front" name such as by screenwriters blacklisted in Hollywood in the 1950s and 1960s.

Age

In many cultures, people go by several different nicknames over the course of their lives. In some cases, a rite of passage or puberty marks the transition from a "milk name" to an adult name. Enrollment in school is another occasion where a child's formal or legal name would begin to be used.

Monarchies

In many monarchies, the sovereign is allowed to choose a regnal name by which he or she will be known. This official name may differ from his or her first name and may not even be one of his or her given names at birth.

A sovereign may choose not to use his or her first name for many reasons. Some, such as George VI of the United Kingdom (born Albert Frederick Arthur George), may wish to make a connection between their reign and that of a previous sovereign (in his case, his father, George V). Others, such as Queen Victoria (born Alexandrina Victoria of Kent), may never have been known by their original first name. Other sovereigns might select a regnal name to emphasize the legitimacy of the succession or even to indicate a change in policy or religion.