What's calendaring?

Calendaring doesn't mean putting things on a calendar, what it means is "adjusting a schedule to take into account working and non-working times and days".

For example, in North America few people work on Saturdays and Sundays. In addition a typical work day is 8 hours.

So a 16 hour project that starts on a Friday, would involve 8 hours on Friday and another 8 hours on Monday.

This ability to skip non-working time is critical to making realistic schedules.