The Collaborative International Dictionary of English v.0.48:

-gen \-gen\ [(1) From Gr. -gen-, from the same root as ge`nos
   race, stock (see Genus). (2) From Gr. suffix -genh`s born.
   Cf. F. -g[`e]ne.]
   1. A suffix used in scientific words in the sense of
      producing, generating: as, amphigen, amidogen, halogen.
      [1913 Webster]

   2. A suffix meaning produced, generated; as, exogen.
      [1913 Webster]

WordNet (r) 3.0 (2006):

gen
    n 1: informal term for information; "give me the gen on your new
         line of computers"

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

gen
 /jen/, n.,v.

    Short for generate, used frequently in both spoken and written contexts.


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

generate
gen

   To produce something according to an algorithm or program or
   set of rules, or as a (possibly unintended) side effect of
   the execution of an algorithm or program.

   The opposite of parse.

   [Jargon File]

   (1995-06-15)