ولا يوصف بالماهية أي المجانسة للأشياء
Nor is He described by quiddity in the sense of sharing a genus with things.
The technical discussion of māhiyyah concerns the question mā huwa?—“what is it?” In classical logic, an answer may situate something within a genus and distinguish its species by a differentia.
For example, a human can be classified within a broader genus and characterized by a distinguishing feature. God is not a member of such a classificatory genus, separated from similar divine members by a species-differentia.
Thus the denial here specifically targets genus-based quiddity and creaturely classification. It must not be mistaken for a denial that God truly exists.