A pseudonym (ˈsjuːdənɪm; ) or alias (ˈeɪli.əs) is a fictitious name that a person or group assumes for a particular purpose, which differs from their original or true name (orthonym). This also differs from a new name that entirely or legally replaces an individual's own. Many pseudonym holders use pseudonyms because they wish to remain anonymous, but anonymity is difficult to achieve and often fraught with legal issues.
Pseudonyms include stage names, user names, ring names, pen names, aliases, superhero or villain identities and code names, gamer identifications, and regnal names of emperors, popes, and other monarchs. In some cases, it may also include nicknames. Historically, they have sometimes taken the form of anagrams, Graecisms, and Latinisations.
Pseudonyms should not be confused with new names that replace old ones and become the individual's full-time name. Pseudonyms are "part-time" names, used only in certain contexts: to provide a more clear-cut separation between one's private and professional lives, to showcase or enhance a particular persona, or to hide an individual's real identity, as with writers' pen names, graffiti artists' tags, resistance fighters' or terrorists' noms de guerre, computer hackers' handles, and other online identities for services such as social media, online gaming, and internet forums. Actors, voice-over artists, musicians, and other performers sometimes use stage names, for example, to better channel relevant energy, gain a greater sense of security and comfort via privacy, more easily avoid troublesome fans/"stalkers", or to mask their ethnic backgrounds.
In some cases, pseudonyms are adopted because they are part of a cultural or organisational tradition; for example, devotional names are used by members of some religious institutes, and "cadre names" are used by Communist party leaders such as Trotsky and Lenin.
A collective name or collective pseudonym is one shared by two or more persons, for example, the co-authors of a work, such as Carolyn Keene, Erin Hunter, Ellery Queen, Nicolas Bourbaki, or James S.