DuckCorp Dico

Found one definition

1.                 From The Jargon File (version 4.4.7, 29 Dec 2003):
                   
   
   
                   
                     
   open
    n.
       Abbreviation for ‘open (or left) parenthesis’ — used when necessary to
       eliminate oral ambiguity. To read aloud the LISP form (DEFUN FOO (X) (PLUS
       X 1)) one might say: “Open defun foo, open eks close, open, plus eks one,
       close close.”