When used as a marked calendar, a calendar indicates what days to run or not to run a particular job. Three calendars are automatically set up when you install the system. They are STANDARD, WORKDAYS and HOLIDAY all are in the system wide default directory.
Windows/OpenVMS:
Schedule> create/calendar my_special_calendar /flags=noholiday /mark=x /date=12-may-2013 
UNIX/Linux:
Schedule> mkcal my_special_calendar -flags=noholiday -mark=x -date=12-may-2013 
What it does: Creates a calendar with Holidays disabled and marks an X on March 12, 2013
Some of the commonly used qualifiers are listed
Windows/OpenVMS  | 
UNIX/Linux  | 
Description  | 
/comment=``any text string''  | 
-comment=``any text string''  | 
Any descriptive text string. Up to 100 characters.  | 
/workdays  | 
-workdays  | 
Only workdays are recognized  | 
/flags = [no]holiday_runs  | 
-flags = [no]holiday_runs  | 
Set flags for whether holidays are allowed as scheduling days.  | 
See Create a calendar (create/calendar or mkcal) for a detailed description of this command.