What is No-Self and what is the Self?

First, a little lesson. In Chan Buddhism (Also known as Zen) we have something known as the two truths doctrine. Something can be ontologically true on one level, the common level, but ontologically untrue on another, and vice versa.

Think of it this way. You have a self, a literal physical three dimensional fact. It is your body, which includes your thoughts (also part of your body.) Then you have what you think of as your "Self," which is an abstract idea which we conflate with some essential representation of us, the "ego." On one level, you have a Self, on another level, there is no Self. Two truths.

Then there's consciousness. Through the experience of non-duality we realise that consciousness is the fundamental aspect of the universe, the fundamental aspect of all things, what we call "God" or "Brahman."

The first self, what can be actually said to be your self, is simply a fruit of karma, the interdependence of all things. It is cause and effect. Genetics, experiences, every injury you've had, every experience you've had, formed your psyche and your body.

On the other hand it is empty, for all things in the universe are fundamentally one, God or the Way or Buddha nature, which is without quality, by necessity. It encompasses all things and nothing.

No self is the realisation that what you actually are, is consciousness, God, emptiness. And yet your body is also your self, on a lower level, the two truths!

We can tie it in further with other ideas. Zhuangzi and Laozi for example both say that we only experience suffering because we "have a self," and that we can only experience lasting happiness when we do not stake ourselves on something but rather recognise we're the universe. From the perspective of an enlightened person, they realise their self is illusory and their body is a mere result of karma, then they turn around and live through their body anyway. This is the dance. Nirvana is Samsara.