أنها لا تنتهي إلى حد لا يتصور فوقه آخر
They do not terminate at a limit beyond which no further term can be conceived.
One meaning of the unboundedness of numbers is that for any number we can conceive a larger one. That does not require all numerals or possible numbers to exist as one completed physical causal collection.
The text extends this distinction to numbers, things known, and things within power. It is a philosophical contrast between unbounded extendibility and an actually completed causal totality; other philosophical treatments of infinity are possible.