This is the average number of days in each year taken over the full cycle of leap days / months, even though the calender may not have been in operation long enough to complete the first cycle.
This is the number of periods of a length close to the lunar cycle into which the year is divided. The name 'month' may not be used by the calendar in question.
This is a short explanation of the way in which the year length is corrected to match the tropical year. This is usually done by inserting an extra day into the calendar at regular intervals. Years when this happens are known as 'Leap Years'.