Fasting Arafah is the fasting sunnah which was held on the day of Arafah that is the 9th of the month Dhul-Hijjah on the calendar of Islam Qamariyah / Hijriyah. Fasting is highly recommended for Muslims who do not perform the pilgrimage.
As for the benefits or virtues of fasting on the day of Arafat 9 Dzulhijjah based on the following hadith:
صوم يوم عرفة يكفر سنتين ماضية ومستقبلة وصوم عاشوراء يكفر سنة ماضية
The fast of the day of'Arafah atoned for sin a year ago and a year to come and the fast of Ashura (10 Muharram) atone for the past year. (HR Ahmad, Muslim and Abu Daud from Abi Qotadah)
