At Sāvatthī.

Then a mendicant went up to the Buddha and said to him:

“Sir, they speak of this thing called ‘ignorance’. What is ignorance? And how is an ignorant person defined?”

“Mendicant, it’s when an unlearned ordinary person doesn’t understand form, its origin, its cessation, and the practice that leads to its cessation. They don’t understand feeling … perception … choices … consciousness, its origin, its cessation, and the practice that leads to its cessation.

This is called ignorance. And this is how an ignorant person is defined.”