The first month of Lunar or Hijree Calendar.It is used officially in Saudi Arabia and in other parts of the world by muslims for fixing the dates of Ramadhan,Hajj etc.
There are two groups of nationally recognized holidays in Oman: Islamic calendar holidays and Gregorian calendar holidays. The Islamic holidays are Islamic New Year (1 Muhurram), Prophet's Birthday (12 Rabi-ul-Awwal), Prophet's Ascension (27 Rajab), End of Ramadan (1 through 3 Shawwal), and Feast of the Sacrifice (10 through 13 Dhu al-Hijjah). The Gregorian holidays are New Year's Day (January 1), Renaissance Day (July 23), and National Day (November 18).
Islamic calendar different than the georgian calendar....There is a difference of 11 days each year;islamic year is shorter than georgian year...For example if this year 1st muharram was on 1st jan next year it will be on 19th or 20th december depending on the lunar cycle and the next islamic year will start on 9th december and so on respectively.....Muharram is the first month of the islamic year it comes after the month of zilhaj