المعنى الاصطلاحي :

The one who is not apt to be diversified or divided for being only one.

الشرح المختصر :

"Al-Wāhid bi al-‘Ayn" (the One in specific) is the One Whose existence prevents the existence of partnership in Him. He is not apt to be diversified. Other similar expressions are: the One in essence and the One in person. They defined that term by saying that it refers to the One, the conception of whom cannot be shared by someone else. It is a compound term that has not been mentioned, neither in the Qur’an, nor in the Sunnah nor in the words of the Companions. Rather, it is a term that was innovated by the philosophers when discussing multitude and oneness. Then, the term was used by scholastic theologians. The term that both of them use frequently is the One in number. They have confused thoughts about the existence of the Creator and that of the creatures. That confusion reached the extent that made them believe that the existence of creatures is the existence of the Creator. Hence, they were the most misguided among people, because they believed that since all existing entities share the quality of existence, therefore, existence of all is the same. They did not differentiate between the One in specific and the one in kind. All existing entities definitely share the quality of existence in general, however, when considering the individuals constituting such existing entities, one will realize how each individual is different from the other. Consequently, the existence of Allah, the Almighty, is different from the existence of creatures.