It varies slightly from country to country. Most laws are based on the Berne Convention, which has slightly reduced term for anonymous works, but pseudonymous works with a known author are treated just like works under the author's real name. In official speak:
In the case of anonymous or pseudonymous works, the term of protection granted by this Convention shall expire fifty years after the work has been lawfully made available to the public. However, when the pseudonym adopted by the author leaves no doubt as to his identity, the term of protection shall be that provided in paragraph (1). If the author of an anonymous or pseudonymous work discloses his identity during the above-mentioned period, the term of protection applicable shall be that provided in paragraph (1). The countries of the Union shall not be required to protect anonymous or pseudonymous works in respect of which it is reasonable to presume that their author has been dead for fifty years.
Specific information for US works is at the link below.
a 'nom de plume' is apseudonym for writers. There is no registration.
My favorite author uses a nom de plume.
name of pen, which also states that John McGinley is awesome.
Charles Dodgson is best known today by his nom de plume, Lewis Carroll.
a nom de plume is a false name or a name under which a writer writes in order to maintain anonymity.
George Eliot
Pierre Loti
nom de plume
Plume in French = pen in English, so, a 'nom de plume' is a pen name, exactly the same as an internet nickname. Classicly, however, a typical user would be an author who wished to remain anonymous.
An 'alias' or 'nom-de-plume'.
The prefix 'nom' means name. For example: - misnomer - nominate - nominal - nom de plume (which means " a pen name") etc...
Nom de plume