وأما الكلي: فهو ما لا يمنع نفس تصوره عن وقوع الشركة فيه، وعن صدقه على كثيرين
A universal is a concept whose very conception does not exclude sharing in it or predicating it of many individuals.
A universal need not actually possess many existing instances. It suffices that the concept itself does not preclude multiple instantiation. “Human” applies to Zayd, ʿAmr and others, without any one's unique personal identity being part of the nature signified.
For a particular, the meaning itself bars plurality; for a universal, the meaning itself does not.