Anno Hegirae

The Hijri year (Arabic: سَنة هِجْريّة‎‎) or era (التقويم الهجري at-taqwīm al-hijrī) is the era used in the Islamic lunar calendar, which begins its count from the Islamic New Year in 622 CE. During that year, Muhammad and his followers migrated from Mecca to Yathrib (now Medina). This event, known as the Hijra, is commemorated in Islam for its role in the founding of the first Muslim community (ummah).

In the West, this era is most commonly denoted as AH (Latin: Anno Hegirae, /ˈænoʊ ˈhɛdʒᵻriː/, "in the year of the Hijra") in parallel with the Christian (AD) and Jewish eras (AM) and can similarly be placed before or after the date. In Muslim countries, it is also commonly abbreviated H ("Hijra") from its Arabic abbreviation hāʾ (). Years prior to AH 1 are reckoned in English as BH ("Before the Hijra"), which should follow the date.

...
Wikipedia