It's the Prajna Paramita.
One of the most famous sutras. Equally commonly recited by the Hinayana and Mahayana Buddhists.
It is the basis upon how Avalokiteshvara the Compassionate Buddha, upon introspection, realises that everything is Empty. And yet Emtpiness is Form and Form is Emptiness.
I personally find this big long sutra very meaningful.
But difficult to understand.