The Hajj (Arabic: حج, transliteration: Ḥaǧǧ) is a pilgrimage to Mecca. It is the largest annual pilgrimage in the worl. It is the fifth pillar of Islam, an obligation that must be carried out at least once in their lifetime by every able-bodied Muslim who can afford to do so. It is a demonstration of the solidarity of the Muslim people, and their submission to God (Arabic: Allah). The pilgrimage occurs from the 10th to the 15th day of Dhu al-Hijjah, the 12th month of the Islamic calendar. Because the Islamic calendar is a lunar calendar, the event cannot be exactly matched to the Gregorian calendar, whose (solar) year is eleven days longer. In 2007, the Hajj took place from December 17 to December 21. The next one will begin in the first week of December 2008.