AH

   abbreviation for the Latin anno hegirae, traditionally used in the West to designate years of the Islamic calendar. The Islamic calendar is lunar, counting twelve lunar months to the year (see month²). Thus its years are shorter than ordinary solar years. Years are counted from the day of the Hijra (Hegira in Latin), the flight of Mohammed from Mecca to Medina, which is fixed at 16 July 622 AD in the Julian calendar. The Islamic year AH 1431 begins at sunset of 13 December 2009 in the current (Gregorian) calendar.

   Link: Islamic calendar information from http://IslamicFinder.org.