A pseudonym is a fictitious name most often associated with authors, though actors, singers, rappers, and even those in organized crime often use a pseudonym in lieu of the birth name.

Pseudonyms are also used for practical reasons when the real name is not known, as in the case of the County Coroner labeling an unidentified body as a "John Doe" or a "Jane Doe".

Pseudonyms, or pen-names, are used in literature for a number of reasons, but most importantly for marketing. An author's readership expects his or her books to fall within a specific genre. If the author pens a novel outside that genre a pseudonym will keep the work separate. That way, the writer can build a fan base in both genres without disappointing fans with work that falls outside the realm of expectation. This facilitates fan loyalty, which translates to sales, and that keeps publishers happy.