A lunar calendar is a calendar that is based on cycles of the lunar phases. Because there are slightly more than twelve lunations in a solar year, the period of 12 lunar months (354.37 days) is sometimes referred to as a lunar year. A common purely lunar calendar is the Islamic calendar or Hijri Qamari calendar. A feature of the Islamic calendar is that a year is always 12 months, so the months are not linked with the seasons and drift each solar year by 11 to 12 days. It comes back to the position it had in relation to the solar year approximately every 33 Islamic years.