The Islamic lunar calendar, also known as the Hijri calendar, is a calendar based on the phases of the moon. It consists of 12 months, totaling about 354 or 355 days in a year, which is shorter than the solar year used in the Gregorian calendar. Each month begins with the sighting of the new moon, making it essential for determining important dates in the Islamic faith. The Islamic calendar is used primarily for religious purposes, such as marking the month of Ramadan, the time of Hajj, and other significant events. The months include Muharram, Safar, Rabi' al-Awwal, and others, each holding cultural and spiritual significance for Muslims around the world.