A pseudonym is a name or identity used by an individual, or group of individuals, which differs from the original and true name of the user(s). It is very similar to a false identity, and is used for a particular purpose.
Pseudonyms include stage names, aliases, nicknames, pen names and other identities. These are usually used to protect or hide the true identity of the user(s); for personal, legal, or other reasons.
An example of an existing pseudonym is Robert Gailbraith. This is a pen name used to publish mystery/thriller novels by the author Joanne Kathleen Rowling, who wrote the Harry Potter series and accompanying books.