The Hijri year or era is the era used in the Islamic lunar calendar, beginning its count from 622 ce, the year of the migration of Muhammad and his followers from Mecca to Yathrib (later Medina), an event known as the Hijra. It is denoted in Arabic with a hāʾ (هـ), the first letter of Hijra. It is denoted in English by the abbreviation AH, which follows the format of the Dionysian era in representing a Latin phrase. Anno Hegirae (/ˈænoʊ ˈhɛdʒᵻriː/) means “in the year of the Hijra” and should technically precede dates in the manner of ad. More commonly, it is placed after the year.
Because the Islamic lunar calendar has only 354 days in its year, it slowly rotates within the Gregorian year. The year 2016 ce corresponds to the Islamic years ah 1437 – 1438.