According to search-discovered classical Islamic scholarship, the concept of **Al-Ghaib (الغيب)**, or 'the Unseen,' refers to the entirety of reality that is concealed and lies beyond the limits of human sensory perception. This fundamental Islamic principle, mentioned 60 times in the Quran, encompasses divine realities such as the essence of Allah, angels, jinn, the events of the Day of Judgment, and Paradise and Hellfire. Classical commentators like Ibn Kathir and At-Tabari synthesize the Quranic verses to categorize the unseen into two types: the **Absolute Unseen (Al-Ghaib al-Mutlaq)**, knowledge of which is exclusive to Allah, such as the 'Five Keys' mentioned in the Hadith of the Prophet Muhammad ﷺ; and the **Relative Unseen (Al-Ghaib al-Nisbi)**, which may be hidden from some but known to others, or which Allah chooses to reveal to His Messengers. Belief in Al-Ghaib is the first defining characteristic of the pious mentioned in Surah Al-Baqarah (2:3), making it a non-negotiable cornerstone of faith (Iman) that tests a believer's trust in divine revelation over empirical evidence.