The 99 names of Allah (arabic Asma Al-ḥusna), are the Names of Allah by which Muslims regard Allah and which are described in the Qur'an, and Sunnah, amongst other places. There is, according to hadith, a special group of 99 names but no enumeration of them. Thus the exact list is not agreed upon, and the Names of Allah exceed 99 in the Qur'an and Sunnah.
According to a hadith narrated by Abdullah ibn Mas'ud some of the names of God have been hidden from mankind, therefore there are not only 99 names of God but there are more.
"The most beautiful names belong to Allah (God): so call on Him by them; ..." (quran 7:180)