The Collaborative International Dictionary of English v.0.48:

Hol \Hol\, a. [See Whole.]
   Whole. [Obs.] --Chaucer.
   [1913 Webster]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

HOL
       Head Of Line


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

HOL

   Higher Order Logic.  A proof-generating system for higher
   order logic based on LCF.  Implementations include HOL-88
   and HOL-90.

   (ftp://ted.cs.uidaho.edu/pub/hol).  Mailing list:
   info-hol@ted.cs.uidaho.edu.

   ["HOL: A Machine Oriented Formulation of Higher Order Logic",
   M.J.C. Gordon, Report 68, Comp Lab U Cambridge (1985)].

   ["Introduction to HOL", M.J.C. Gordon et al, Cambridge U Press
   1993 ISBN 0-521-441897].