A leap week calendar is a calendar system with a whole number of weeks in a year, and with every year starting on the same weekday.
Some, however, such as the ISO week date calendar, are simply conveniences for specific purposes.
[1] The ISO calendar in question is a variation of the Gregorian calendar that is used (mainly) in government and business for fiscal years, as well as in timekeeping.
Leap week calendars vary on whether the concept of month is preserved and whether the month (if preserved) has a whole number of weeks.
The Pax Calendar and Hanke–Henry Permanent Calendar preserve or modify the Gregorian month structure.