What does "no-self" mean in Buddhism?

In Buddhism, no-self (anattā in Pali) means that nothing has a permanent, unchanging self or essence. The word is built from an, "not", and attā, "self-existent essence". It is one of the Three Marks of Existence, together with dukkha, the unsatisfactoriness of life, and anicca, impermanence.

It does not simply say "you don't exist". Scholars describe anattā as a strategy to attain non-attachment by recognising everything as impermanent, while staying silent on the ultimate existence of an unchanging essence. The Buddha is also said to have kept rebirth and karmic responsibility: there is no essence, but there is rebirth, and actions have consequences. The Buddhist target is what is called the "'I am' conceit", the root of self-importance and self-centredness, which only the enlightened are free from.

The idea is easiest to see by contrast. Dominant schools of Hinduism assert an Ātman, a pure awareness or witness-consciousness. Peter Harvey notes that in the Buddhist Suttas literally everything, even Nirvana, is seen as non-Self.

And here is the twist. Some scholars, including Richard Gombrich and Alexander Wynne, argue that the Buddha's statements were originally a "not-self" teaching, that is, a teaching about what should not be taken as self, which later hardened into "no-self". In one text the Buddha stays silent when asked whether there is a self. The monk Thanissaro Bhikkhu goes as far as calling "there is no self" the granddaddy of fake Buddhist quotes. Other Buddhist scholars disagree, so this is a live debate within Buddhism.