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

formal argument
param
parameter

    (Or "parameter") A name in a function or
   subroutine definition that is replaced by, or bound to, the
   corresponding actual argument when the function or
   subroutine is called.  In many languages formal arguments
   behave like local variables which get initialised on entry.

   See: argument.

   (2002-07-02)