atta-kilamatha: 'self-mortification', is one of the two extremes to be avoided, the other extreme being addiction to sensual pleasures (kāma-sukha), whilst the Noble 8-fold Path constitutes the Middle Path (majjhima-paṭipadā, q.v.). See the Buddha's first sermon, "The Establishment of the Realm of Dhamma" (Dhamma-cakkappavattana-Sutta).

Buddhist Dictionary, Manual of Buddhist Terms and Doctrines, by NYANATILOKA MAHATHERA