Definitions for "Nym"
A name used on UseNet or IRC: a "handle" that is not the real name of the person. From either/both pseudonym or anonymous. Like a nom-de-plume for writers, as Mark Twain was the "nym" of Samuel Clements, except he wasn't trying to remain anonymous. In his case it was simply a pseudonym, while on UseNet or IRC (Internet Relay Chat) it is usually used to secure anonymity as the primary function. Nyms are often chosen from books, movies, cartoons, mythology, etc. Chances are if you see someone posting as MarkTwain, his name isn't Mark, or Twain, or Sam, or Clements.
nym is an identifier that cannot be readily linked to the underlying entity. An anonym can't. A pseudonym can't easily. [Source: Roger Clarke.