That is usually called a "pen name." Sometimes people will refer to it as "nom de plume" which essentially means the same thing, only in French. Generally, another good term to know is "pseudonym" which is what a person would call any fake name someone uses. So one could say "He published the book under a pen name" or could also say "He published the book under a pseudonym/."
Pen name or pseudonym is a name used by an author instead of their real name. This can be done for various reasons such as privacy, genre change, or to appeal to a different audience.
"Nom de plume" for the raffinates, "pseudonym" for the rest of us.
http://en.wikipedia.org/wiki/Pen_name
pseudonym
Nom de plume
A pseudonym is a fictitious name used by an author instead of their real name. It is often used in literature or by individuals who wish to remain anonymous or adopt a different identity for various reasons.
Mark Twain is nom de plume (a name used by an author instead of his rea name). It has no middle part. The author who used the name Mark Twain was Samuel Langhorne Clemens.
autonym
None of the signers used a false name.
Richard Bachman's real name is Stephen King. It was a pen name used by the author to publish some of his early works.
Roald Dahl did not use a pen name while writing. Instead, he used his real name that he was born with in Llandaff, Cardiff, Wales.
The real name of the author of Middlemarch is Mary Ann Evans. She used the pen name George Eliot when writing her novels.
Mark Twain was the pen name used by Samuel Clemens, so both names refer to the same person. The book attributing the authorship to Samuel Clemens is simply using his real name instead of his pen name.
A pen name or pseudonym is a fictitious name used by an author instead of their real name when writing and publishing books, articles, or other works. Authors often choose to use a pen name for various reasons, such as privacy, genre differentiation, or marketing purposes.
A pen name is a fake name used by an author if they don't want to give out their real name. A pen isn't real it is called a frindle if you have read the book by Andrew Clements you would know it is called a frindle
A pen name is a pseudonym adopted by an author who does not want his or her own real name to appear on a written work. A pseudonym is a false name used for any purpose.