The Collaborative International Dictionary of English v.0.48:

Plexus \Plex"us\, n.; pl. L. Plexus, E. Plexuses. [L., a
   twining, braid, fr. plectere, plexum, to twine, braid.]
   1. (Anat.) A network of vessels, nerves, or fibers.
      [1913 Webster]

   2. (Math.) The system of equations required for the complete
      expression of the relations which exist between a set of
      quantities. --Brande & C.
      [1913 Webster]

   3. A network; an intricate or interwoven combination of
      elements or parts in a coherent structure.

            In the perception of a tree the reference to an
            object is circumscribed and directed by a plexus of
            visual and other presentations.       --G. F. Stout.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

plexus
    n 1: a network of intersecting blood vessels or intersecting
         nerves or intersecting lymph vessels [syn: plexus,
         rete]

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

Plexus

   A modular web server written in Perl by Tony
   Sanders .  Comes with interfaces to allow
   many other information services to be served via the Web.

   Version 3.0m 1994-07-22 (ftp://ftp.earth.com/plexus/).

   (1994-07-22)