فالأعيان ما أي ممكن يكون له قيام بذاته
Entities are possible beings that can subsist in themselves, in the relevant technical sense.
The qualifier possible matters: the classification concerns contingent beings within the world, not God's essence or attributes. A thing subsisting in itself means it is not understood merely as an attribute existing in some other subject.
A stone can be discussed as a stone, whereas its being hot or cold is a state or accident of that stone. The classification concerns how created things exist, not their freedom from a Creator.