Emptiness

When Buddhist teaching says that things are empty or do not exist as such, what is often meant by "things" or "phenomena" in such statements is things as they are conceived of—the point is then that a name or definition does not encompass or capture a thing, either in its essence or in the totality of possibilities of its conditional existence.

To pursue the matter more deeply, when we consider the idea of the world as conceptions based on perceptions based on sensations, we can see that we have no further direct evidence for anything phenomenal beyond sense. If we seek corroboration of sense by sense, we find that we cannot reach beyond sense, so to speak, except by inference. We cannot therefore directly "apprehend" the objective world; we can only reflect impressions. This "emptiness of ungraspability" is among the major avenues of contemplation leading to authentic appreciation of emptiness.

~Thomas Cleary, in Entry Into the Inconceivable