A lunisolar calendar is a calendar in many cultures whose date
indicates both the moon phase and the time of the solar year. If
the solar year is defined as a tropical year then a lunisolar
calendar will give an indication of the season; if it is taken as a
sidereal year then the calendar will predict the constellation near
which the full moon may occur. As with all calendars which divide
the year into months there is an additional requirement that the
year have a whole number of months. In this case ordinary years
consist of twelve months but every second or third year is an
embolismic year which adds a thirteenth intercalary embolismic or
leap month.