المعنى الاصطلاحي :

Anything that the mind cannot conceive its existence in reality.

الشرح المختصر :

"Mustaheel" (the impossible) is everything that cannot exist in the real world. It is of two types: 1. Impossible per se: What cannot happen or exist and is not conditional on or linked to power. An example is the impossibility of Allah creating someone like Himself. This is because such likeness is impossible. The least to be said about such a case is that Allah is the Creator and the other entity is a creature. Therefore, similarity would not exist in any way. 2. Impossible due to external reasons: What does not normally occur, even if possibly conceived by the mind. It is conditional on and related to power. So, it can happen depending on the ability involved. All the universal miracles of the Prophets fall under this category, like the splitting of the moon for Prophet Muhammad, may Allah's peace and blessings be upon him. This word "mustaheel" is not mentioned in the Qur’an; but the verb "haal" and some of its derivatives do exist in the Book of Allah. It is impossible to conceive that Allah, the Almighty, would possess the opposites of His excellent attributes. For example, ignorance, the opposite of knowledge, is something impossible to exist or conceive as far as Allah, the Almighty, is concerned. The same holds true for incapability and death, which are the opposites of power and everlastingness, respectively.

التعريف اللغوي المختصر :

“Mustaheel”: unattainable, impossible, what combines two contradictions like the existence of one body in two different places at the same time. Other meanings: falsehood.