What does the acronym GNU stand for?

What does the acronym GNU stand for?

• Guaranteed Not Unix
• GNU's Not Unix
• Genuine Non-Unix
• Gratis Not Unix 

EXPLANATION

In computing, an early tradition in the hacker community (especially at MIT) was to choose acronyms and abbreviations that referred humorously to themselves or to other abbreviations. Perhaps the earliest example in this context – from 1960 – is the backronym "Mash Until No Good", which was created to describe Mung, and a while later was revised to "Mung Until No Good". It lived on as a recursive command in the editing language TECO.^[3] In 1977 or 1978 came TINT ("TINT Is Not TECO"), an editor for MagicSix written (and named) by Ted Anderson. This inspired the two MIT Lisp Machine editors called EINE ("EINE Is Not Emacs", German for one) and ZWEI ("ZWEI Was EINE Initially", German for two). These were followed by Richard Stallman's GNU (GNU's Not Unix).
Many others also include negatives, such as denials that the thing defined is or resembles something else (which the thing defined does in fact resemble or is even derived from), to indicate that, despite the similarities, it was distinct from the program on which it was based.^[3]
An earlier example appears in a 1976 textbook on data structures, in which the pseudo-language SPARKS is used to define the algorithms discussed in the text. "SPARKS" is claimed to be a non-acronymic name, but "several cute ideas have been suggested" as expansions of the name. One of the suggestions is "Smart Programmers Are Required to Know SPARKS".^[4] (this example is tail recursive)

SOURCE

https://en.wikipedia.org/wiki/Recursive_acronym