The Collaborative International Dictionary of English v.0.48:

Forum \Fo"rum\, n.; pl. E. Forums, L. Fora. [L.; akin to
   foris, foras, out of doors. See Foreign.]
   1. A market place or public place in Rome, where causes were
      judicially tried, and orations delivered to the people.
      [1913 Webster]

   2. A tribunal; a court; an assembly empowered to hear and
      decide causes.
      [1913 Webster]

            He [Lord Camden] was . . . more eminent in the
            senate than in the forum.             --Brougham.
      [1913 Webster]

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

fora
 pl.n.

    Plural of forum.


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

forum
fora
topic group

    (Plural "fora" or "forums") Any discussion group
   accessible through a dial-in BBS (e.g. GEnie, CI$), a
   mailing list, or a Usenet newsgroup (see network,
   the).  A forum functions much like a bulletin board; users
   submit postings for all to read and discussion ensues.

   Contrast real-time chat or point-to-point personal e-mail.

   [Jargon File]

   (1998-01-18)