WordNet (r) 3.0 (2006):

Yay
    n 1: a branch of the Tai languages

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

YAY
       Yet Another YACC (YACC, Bull)


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

Yet Another Yacc
Yay

    (Yay) An extension of Yacc with LALR2 parsing.

   Yay is available from Bull as part of the University of
   Waterloo Tools package maintained by .

   (1994-11-09)