The Free On-line Dictionary of Computing (19 January 2023):

FOAF

   [Usenet] Friend Of A Friend.  The source of an unverified,
   possibly untrue story.  This term was not originated by
   hackers (it is used in Jan Brunvand's books on urban
   folklore), but is much better recognised on Usenet and
   elsewhere than in mainstream English.

   [Jargon File]


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

FOAF
 //, n.

    [Usenet; common] Acronym for ‘Friend Of A Friend’. The source of an
    unverified, possibly untrue story. This term was not originated by hackers
    (it is used in Jan Brunvand's books on urban folklore), but is much better
    recognized on Usenet and elsewhere than in mainstream English.