When they talk about emptiness in Buddhism, what do they refer to?
I am not really sure, but here is what comes for me:
In my immediate experience, it’s as if all experiences are “empty” like a dream. It’s all happening within and as consciousness. There is the appearance of substantiality, and this is created by the mind (by combining thoughts with sensations).
Since everything to me happens within and as what I am, everything – including this human self – is empty of any separate self. There is no real separation anywhere, and no separate selves.
I also find that any thought is empty of any final or absolute truth. Thoughts have validity in different ways, some are more useful than others in certain situations, and some may even be closer to reality in a certain way, but they cannot reflect any final truth.