It means false name. A fictitious name that is used to hide the true identity.
Pseudonym that is also written pseudonym is the nickname that a person uses to supplant sometimes his true one, the pseudonym is widely used among artists, writers, athletes etc.
Pseudonym for pseudo, 'false, substitute, semi, bad imitation' and Nimo, 'name', fictitious name under which works are published or the real name of an actor, artist or person who must remain anonymous is concealed.