The Islamic calendar, also known as the Hijri calendar, is a lunar calendar used by Muslims around the world to determine the dates of religious events and observances. It consists of 12 months based on the phases of the moon, with each month lasting 29 or 30 days. The year begins with Muharram and ends with Dhul-Hijjah.

Key Islamic dates such as Ramadan, Eid al-Fitr, Eid al-Adha, and the Hajj pilgrimage are determined by this calendar. Unlike the Gregorian calendar, which is solar, the Islamic calendar is about 10 to 12 days shorter, meaning Islamic dates shift each year when compared to the Gregorian calendar.

The Islamic calendar plays a vital role in the spiritual and daily lives of Muslims, guiding them in their religious practices and celebrations. It is also used in various Islamic countries for civil purposes alongside the Gregorian calendar.