The ability of an Identity to keep its Entity secret from everyone. Literally means 'no name'. It must be persistent, which makes it difficult, if not impossible, to remain truly anonymous because details deduced over time may be joined with other details and republished (unless there are privacy laws preventing it). For example, a prepaid mobile phone can allow the purchaser to remain anonymous until a pattern of use is established. Also see Pseudonym.

Source: http://identityaccessman.blogspot.com/2006/08/identity-dictionary.html