Mount Arafat is the most famous and significant mountain known to Muslims. Standing on it is the completion of the greatest pillar of Hajj, and Hajj is invalid without standing on Arafat. 

The Prophet Muhammad (peace be upon him) said:
 "Hajj is (standing at) Arafah. Whoever reaches Arafah before dawn has completed the Hajj."
Narrated by Al-Tirmidhi, Al-Nasa’i, Ibn Majah, and Ahmad. 

It is also mentioned in the Qur'an:
 "There is no blame upon you for seeking bounty from your Lord. But when you depart from Arafat, remember Allah at Al-Mash'ar Al-Haram. And remember Him as He has guided you, for indeed, you were before that among those astray."
(Surah Al-Baqarah: 198) 

Mount Arafat is located on the road between Mecca and Taif. Several reasons have been cited for its name: 

1. It is said that Adam and hawa' met and recognized each other there after descending from Paradise.
2. It is also said that Angel Jibreel guided Prophet Ibrahim, peace be upon them through the sites of Hajj and kept asking him, “Do you recognize (this place)? Do you recognize (this place)?” to which Ibrahim replied, “I recognize it. I recognize it.”
3. Another explanation is that it was named Arafat because people get to know one another there.