WordNet (r) 3.0 (2006):

knowledge base
    n 1: the content of a particular field of knowledge [syn:
         knowledge domain, knowledge base, domain]

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

knowledge base

    A collection of knowledge
   expressed using some formal knowledge representation
   language.  A knowledge base forms part of a knowledge-based
   system (KBS).

   (1994-10-19)