What is "pseudonymity"

Pseudonymity \Pseu`do*nym"i*ty\, n. The using of fictitious names, as by authors.

n. The state of being pseudonymous, of hiding one's true identity behind a pseudonym

Pseudonymity, a word derived from pseudonym, meaning 'false name', is a state of disguised identity. The pseudonym identifies a holder, that is, one or more human beings who possess but do not disclose their true names (that is, legal identities). Most pseudonym holders use pseudonyms because they wish to remain anonymous, but anonymity is difficult to achieve, and is often fraught with legal issues. True anonymity requires unlinkability, such that an attacker's examination of the pseudonym holder's message provides no new information about the holder's true name.