The Islamic calendar or Muslim calendar or Hijri calendar is a lunar calendar used to date events in many predominantly Muslim countries, and used by Muslims everywhere to determine the proper day on which to celebrate Islamic holy days and festivals. It is a lunar calendar having 12 lunar months in a year of about 354 days. Because this lunar year is about 11 days shorter than the solar year, Islamic holy days, although celebrated on fixed dates in their own calendar, usually shift 11 days earlier each successive solar year, such as a year of the Gregorian calendar. Islamic years are also called Hijra years because the first year was the year during which the Hijra occurred. Prophet Muhammad's (PBUH) emigration from Mecca to Medina. Thus each numbered year is designated either H or AH, the latter being the initials of the Latin anno Hegirae (in the year of the Hijra).
The Islamic months are named as follows:
1. Muharram
2. Safar
3. Rabi’al Awal
4. Rabi’al Thaani
5. Jamaada Awal
6. Jamaada Thaani
7. Rajab
8. Sha`ban
9. Ramadãn
10. Shawwãl
11. Dhu-l-qa'adah
12. and Zulhijjah
The Islamic calendar has been used primarily for religious purposes, and has sometimes been used for official purposes as well. Because of its nature as a purely lunar calendar, however, it cannot be used for agricultural purposes and historically Islamic communities have used other calendars for this purpose: the Egyptian calendar was formerly widespread in Islamic countries, and the Iranian calendar and the 1789 Ottoman calendar (a modified Julian calendar) were also used for agriculture in their countries. In Morocco, the ancient Julian calendar is still used by farmers in the countryside. These local solar calendars have receded in importance with the near-universal adoption of the Gregorian calendar for civil purposes. Saudi Arabia is currently the only Muslim country to use the Islamic calendar as the calendar of daily government business.