(lit: influxes), 'cankers', taints, corruption's, intoxicant biases.
There is a list of four (as in D. 16, Pts.M., Vibh.):
the canker of sense-desire (kāmāsava)
of (desiring eternal) existence (bhavāsava)
of (wrong) views (ditthāsava)
of ignorance (avijjāsava)
A list of three, omitting the canker of views, is possibly older and is more frequent in the Suttas, e.g. in M.2, M.9, D.33; A.III.59, 67; A.VI.63.
In Vibh. (Khuddakavatthu Vibh.) both the 3-fold and 4-fold division are mentioned. The fourfold division also occurs under the name of 'floods' (ogha) and 'yokes' (yoga).
Through the path of Stream-Entry, the canker of views is destroyed; through the path of Non-Returning, the canker of sense-desire; through the path of Arahantship, the cankers of existence and ignorance. M. 2 shows how to overcome the cankers, namely, through insight, sense-control, avoidance, wise use of the necessities of life, etc. For a commentarial exposition, see Atthasālini Tr. I, p. 63f: II, pp. 475ff.
Khīnāsava, 'one whose cankers are destroyed', or 'one who is canker-free', is a name for the Arahat or Holy One. The state of Arahantship is frequently called āsavakkhaya, 'the destruction of the cankers'. Suttas concluding with the attainment of Arahantship by the listeners, often end with the words: "During this utterance, the hearts of the Bhikkhus were freed from the cankers through clinging no more" (anupādāya āsavehi cittāni vimuccimsū'ti).