What is non-duality in Buddhism? I noticed some questioners on this site using the term "non-duality".

What is non-duality in Buddhism?

This is a well-known idea in Hinduism i.e. advaita. But does it exist in Buddhism?

Is it an official term in Buddhism, or just a convenient Western philosophy terminology to describe a concept just like the terms "ontology" or "epistemology"?

How is it used in Theravada and Mahayana? What are the Pali and Sanskrit terms for it?

AN 10.29 seems to have the word "advayam" which Bhikkhu Sujato translates as "non-dual" but Bhikkhu Bodhi translates as "undivided". Not sure if this is related.
There's a post here on that subject, which isn't long but difficult to summarise: The Dharma of Non-Duality

In the first (main) part the author says:


The word for "non-duality" is advaita
The Buddha didn't use that term (because it was already used then to mean "union of soul with God")
The Buddha did teach "non-duality" is many ways -- e.g. "neither self nor no-self", "middle way", "form and emptiness" (in the Heart Sutra), and "dependent origination implies neither self nor other"
Nagarjuna "used non-duality" in his Mulakarika
Etc.


In a second part (posted as a long comment on the first part), Hans Gruber argues that neither Nargajuna nor the Buddha teach non-duality:


Non-clinging isn't non-duality
Emptiness isn't non-duality, and different things are different even if they are dependently originated
Moving towards liberation (by reducing ignorance etc.) isn't non-duality
The Buddha didn't teach non-dualism as a metaphysical principle, instead he taught dependent origination (also didn't teach anatta as a metaphysical principle or abstract terms, but only as a "predicate" or "practice instruction" applicable to concrete terms i.e. any and all dhammas).


AN 10.29 seems to have the word "advayam" which Bhikkhu Sujato translates as "non-dual" but Bhikkhu Bodhi translates as "undivided". Not sure if this is related.

Yes I expect it's the same root: a+dvaya ("not a pair").

Looking at advaita compared with advaya reminds me of, I wonder if it's similar to, tatha versus tathata -- where one is the adjective (e.g. "true" or "non-dual, single") and the other is an abstract noun ("truth, suchness" or "non-duality") -- or Suñña versus Suññata i.e. "empty" versus "emptiness".

That might fit with Hans Gruber's saying that the Buddha didn't non-duality as a principle (e.g. as an abstract noun).