المعنى الاصطلاحي

Something that cannot be logically expected to happen or exist in the real world.

الشرح المختصر

"Mustaheel al-wujood" (impossible to exist) is what cannot logically happen or exist in the real world. It is of two types: 1. Intrinsical "mustaheel al-wujood": something of which the existence is inherently impossible and which is irrelevant with regard to the Power of Allah. For example, it is impossible for Allah, the Almighty, to create a god like Himself, because similarity here is inherently impossible. Simply, we can prove this by saying that the new god is a creature, while our Lord is the Creator, which renders similarity absolutely void. 2. Extrinsical "mustaheel al-wujood": something which is usually impossible to exist or occur, yet rationally possible. The power of Allah, the Almighty, is relevant to this type, as its real existence is contingent upon His Power. All cosmic miracles of prophets, peace be upon them all, fall under this type, such as the splitting of the moon as a miracle of Prophet Muhammad, may Allah’s peace and blessings be upon him. The word "mustaheel" (impossible) has not been mentioned in the Qur’an, however, the verb "hāla" (separate) and some of its conjugations has been mentioned in it. The opposites of confirmed Attributes of Allah, the Exalted, are impossible for Him; for example, Knowledge, Power, and Life are attributes of Allah; therefore, their opposites (ignorance, weakness, and death) are impossible for Him.

التعريف

What is not possible to exist. It is what reason rules to be non-existent and does not allow the possibility of its existence in any situation one can imagine, such as the impossibility of two opposites to be present at the same place and time.