Which is the correct "code/word" for Language Neutral? I read an article from Gábor Hojtsy where he says:


  Language neutral uses the language code 'und', which means undefined
  and is specified to be used for such cases by the ISO 639 standard.


But when you go to read the ISO 639 you can find:


  und, for "undetermined";


And you can find inside Drupal the "Language Neutral"

I ask the question because I'm writing a module where I need to have a word to identify the nodes that don't have a defined language. So, which is the word to use, Neutral, Undefined or Undetermined?
From Drupal constant LANGUAGE_NONE api documentation Und stands for undetermined and in Drupal 8 it is called LANGCODE_NOT_SPECIFIED