Ultimate reality

Ultimate reality, or absolute reality, is defined as everything that actually exists whether or not it is observable, accessible or understandable by science or philosophy or any other human technique. Thus some part of the nature of ultimate reality may be, by definition, unknowable. However the philosophical discipline of metaphysics investigates, so far as it may be investigated, this question. See reality.

This raises questions:

• What is meant by "actually exists"? Is there any definition for or even understanding of "actually exists" that is not circular?

• What is the difference between ultimate reality and reality?