means After Hijrah. It is the reference used in the Islamic calender, instead of A.D. which is used in the Christian calender.
means migration. The Hijrah refers to the Prophet's migration from Mecca to Madinah. This journey took place in the twelfth year of his mission (622 C.E.). This is the beginning of the Muslim calendar. The word hijrah means to leave a place to seek sancturary or freedom from persecution or freedom of religion or any other purpose. Hijrah can also mean to leave a bad way of life for a good or more righteous way.
The migration in 622 C.E. of Prophet Muhammad and members of the Muslim community from the city of Makkah to the city of Yathrib, later renamed Madinah an-Nabi (city of the Prophet) in honor of Muhammad. The Islamic lunar calendar, often called the Hijri calendar, is dated from this important event, which marks the beginning of an Islamic state (in Madinah) in which the Shari'ah (Islamic Law) was implemented.