A lunar calenar is a calendar that is based on cycles of the moon phase. The only widely used purely lunar calendar is the Islamic calendar, whose year always consists of 12 lunar months. A feature of a purely lunar year, on the Islamic calendar model, is that the calendar ceases to be linked to the seasons, and drifts each year by 11 or 12 days, and comes back to the position it had in relation to the solar year every 33 or 34 Islamic years. It is used predominantly for religious purposes. In Saudi Arabia it is also used for commercial purposes.