Exonym

Full Title or Meme

An Exonym is a name given to an entity by a foreign source, often in a different language or alphabet.

Many web sites require users to have a persistent user name which is unique on their site to identify the user in the language used by te site.
Wikipedia defines Exonym as a common, external name for a geographical place, group of people, individual person, or a language/dialect, that is used only outside that particular place, group, or linguistic community. Exonyms exist not only for historico-geographical reasons, but also in consideration of difficulties when pronouncing foreign words.

Users may wish to have some name that is not associated with their real name when the web site requires a persistent user name or they may wish to have separate Personas associated (e.g.) with their social self and their work self.
In contexts where names are not validated (of low Assurance) the problem arises that trolls many adopt the name of some well-known person to be able to make statements that falsely appear to be from the real person.^[1]

Users are often asked to use their email address as a local user name since the email address is known to be a URI and hence unique in the internet, at least for a period of time.
When the user has an option, they often pick some sort of description name, such as a gamertag in a role playing game, which is tested for uniqueness within the relevant name domain.
When a user needs to provide some sort of validated attribute for the duration of a session at a web site, a session ID might provide sufficient security to bind the verified attribute for the session duration.

↑ Jack Nicas, Oprah, Is That You? Most Likely, It's Not. 2018-07-08 New York Times page BU1