”impurities”, corruptions, imperfections (a frequent rendering by ”defilements” is better reserved for kilesa, q.v.).
A list of 16 moral ”impurities of the mind” (cittassa upakkilesa) is mentioned and explained in M. 7 & 8 (WHEEI. 61/62): 1. covetousness and unrighteous greed (abhijjha^-visamalobha), 2. ill will (vya^pa^da), 3. anger (kodha), 4. hostility (upana^ha), 5. denigration (makkha), 6. domineering (pala^sa), 7. envy (issa^), 8. stinginess (macchariya), 9. hypocrisy (ma^ya^), 10. fraud (sa^theyya), 11. obstinacy (thambha), 12. presumption (sa^rambha), 13. conceit (ma^na), 14. arrogance (atima^na), 15. vanity (mada), 16. negligence (pama^da).
There are 3 groups of upakkilesa pertaining to meditation:
(a) 9 mental imperfections occurring in ”one devoted to higher mental training” (adhicitta); 3 coarse ones - evil conduct in deeds, words and thoughts; 3 medium - thoughts of sensual desire, ill will and cruelty; 3 subtle - thoughts about one”s relatives, one”s country and one”s reputation (A. III, 100).
(b) 18 imperfections in the practice of mindfulness of breathing (a^na^pa^na-sati, q.v.), mentioned in Pts.M., a^na^pa^na-katha^ (tr. in Mindfulness of Breathing, by n~a^namoli Thera (p. 60; BPS).
(c) 10 ”imperfections of insight” (-meditation, vipassanúpakkilesa); s. visuddhi V.