calendar-date-display-form

calendar-date-display-form is a variable defined in `calendar.el'.
Its value is

((if dayname
     (concat dayname ", "))
 monthname " " day ", " year)

• This variable may be risky if used as a file-local variable.

Documentation:
Pseudo-pattern governing the way a calendar date appears.
Used by the function `calendar-date-string' (which see), a pseudo-pattern
is a list of expressions that can involve the keywords `month', `day',
and `year' (all numbers in string form), and `monthname' and `dayname'
(both alphabetic strings). For example, a typical American form would be

'(month "/" day "/" (substring year -2))

whereas

'((format "%9s, %9s %2s, %4s" dayname monthname day year))

would give the usual American style in fixed-length fields. The variables
`calendar-iso-date-display-form', `calendar-european-date-display-form', and
`calendar-american-date-display-form' provide some defaults for three common
styles.

You can customize this variable.