Nom de plume is a name under which authors write which is not their real name: “O. Henry is the nom de plume for the short story writer William Sydney Porter . ”
Pen name is the name an author assumes which is not the author’s real name: “George Eliot was the pen name of Mary Ann Evans.”
Pseudonym is a false or fictitious name: “Balraj Dutt acted in the films under the pseudonym of Sunil Dutt who later married Nargis.”