Kleshas (kleśa; किलेस kilesa; ཉོན་མོངས། nyon mongs), in Buddhism, are mental states that cloud the mind and manifest in unwholesome actions. Kleshas include states of mind such as anxiety, fear, anger, jealousy, desire, depression, etc. Contemporary translators use a variety of English words to translate the term kleshas, such as: afflictions, defilements, destructive emotions, disturbing emotions, negative emotions, mind poisons, and neuroses.
In the contemporary Mahayana and Theravada Buddhist traditions, the three kleshas of ignorance, attachment, and aversion are identified as the root or source of all other kleshas. These are referred to as the three poisons in the Mahayana tradition, or as the three unwholesome roots in the Theravada tradition.
While the early Buddhist texts of the Pali canon do not specifically enumerate the three root kleshas, over time the three poisons (and the kleshas generally) came to be seen as the very roots of samsaric existence.
In the Pali Canon's discourses (sutta), kilesa is often associated with the various passions that defile bodily and mental states. In the Pali Canon's Abhidhamma and post-canonical Pali literature, ten defilements are identified, the first three of which – greed, hate, delusion – are considered to be the "roots" of suffering.
In the Pali Canon's Sutta Piṭaka, kilesa and its correlate upakkilesa are affective obstacles to the pursuit of direct knowledge (abhijñā) and wisdom (pañña).
For instance, the Samyutta Nikaya includes a collection of ten discourses (SN 27, Kilesa-sayutta) that state that any association of "desire-passion" (chanda-rāgo) with the body or mind is a "defilement of mind" (cittasse'so upakkileso):
"Monks, any desire-passion with regard to the eye is a defilement of the mind. Any desire-passion with regard to the ear... the nose... the tongue... the body... the intellect is a defilement of the mind. When, with regard to these six bases, the defilements of awareness are abandoned, then the mind is inclined to renunciation.