The Collaborative International Dictionary of English v.0.48:

Trilogy \Tril"o*gy\, n. [Gr. trilogi`a; pref. tri- (see Tri-)
   + lo`gos speech, discourse: cf. F. trilogie.]
   A series of three dramas which, although each of them is in
   one sense complete, have a close mutual relation, and form
   one historical and poetical picture. Shakespeare's " Henry
   VI." is an example.
   [1913 Webster]

         On the Greek stage, a drama, or acted story, consisted
         in reality of three dramas, called together a trilogy,
         and performed consecutively in the course of one day.
                                                  --Coleridge.
   [1913 Webster] Triluminar

WordNet (r) 3.0 (2006):

trilogy
    n 1: a set of three literary or dramatic works related in
         subject or theme

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

Trilogy

    A strongly typed logic programming language
   with numerical constraint-solving over the natural
   numbers, developed by Paul Voda 
   at UBC in 1988.  Trilogy is syntactically a blend of
   Prolog, Lisp, and Pascal.  It contains three types of
   clauses: predicates (backtracking but no assignable
   variables), procedures (if-then-else but no backtracking;
   assignable variables), and subroutines (like procedures, but
   with input and system calls; callable only from top level or
   from other subroutines).

   Development of Trilogy I stopped in 1991.  Trilogy II,
   developed by Paul Voda 1988-92, was a declarative general
   purpose programming language, used for teaching and to write
   CL.

   (http://fmph.uniba.sk/~voda).

   ["The Constraint Language Trilogy: Semantics and
   Computations", P. Voda, Complete Logic Systems, 741 Blueridge
   Ave, North Vancouver BC, V7R 2J5].

   (2000-04-08)