Pseudonymity is the near-anonymous state in which a user has a consistent identifier that is not their real name: a pseudonym. In pseudonymous systems, real identities are only available to site administrators.
Pseudonymity allows users to communicate with one and other in a generally anonymous way. Pseudonyms are typically user-chosen names. Pseudonymity helps maintain user privacy and enables free speech without security worries.
Very few sites and services are really anonymous, but there are varying degrees of anonymity. Facebook, for example, requires individuals to use their real names. On some forums and other venues, the user’s pseudonym and IP address may be displayed along with location information, which can make their identity relatively easy to detect.
Anonymity cannot be assured even if only site owners have information that links users to their posts and the identifying information is encrypted. All encryption can be broken, given sufficient time and compute resources. Furthermore, there are so many ways to link users to their true identities that most anonymity on the web can be said to be either pseudonymity or pseudo-anonymity. Pseudo-anonymity contrasts with pseudonymity in that it allows users to post or comment without the use of any type of identifier.