The Jargon File (version 4.4.7, 29 Dec 2003):

grilf
 //, n.

    Girlfriend. Like newsfroup and filk, a typo reincarnated as a new word.
    Seems to have originated sometime in 1990 on Usenet. [A friend tells me
    there was a Lloyd Biggle SF novel Watchers Of The Dark, in which alien
    species after species goes insane and begins to chant ?Grilf! Grilf!?. A
    human detective eventually determines that the word means ?Liar!? I hope
    this has nothing to do with the popularity of the Usenet term. ?ESR]


The Free On-line Dictionary of Computing (30 December 2018):

grilf

   Girl-friend.

   Like newsfroup and filk, a typo incarnated as a new word.
   Seems to have originated sometime in 1992.

   [Jargon File]

   (1995-01-31)