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Upekkha is a sanskrit and Pali word meaning equanimity. The opposition between comfortable sensations and uncomfortable ones disappears. More especially, it is one of the fourth Jhana's factor, present only in this Jhana. Wikipedia does not yet have an article with this exact name. ... In psychology, sensation is the first stage in the chain of biochemical and neurologic events that begins with the impinging of a stimulus upon a sensory organ, and leads to perception, the sort of mental state that is reflected in statements like I see a uniformly blue wall. ... Dhyāna means meditation in Sanskrit. ...
In the fifth stage of jhana there is upekkha instead of somanassa, and therefore eight lokuttara jhanacittas, accompanied by the jhana-factors of the fifth stage, are not accompanied by somanassa but by upekkha.
Upekkha also accompanies the two types of moha-mula-citta which are: moha-mula-citta accompanied by vicikiccha (doubt) and moha- mula-citta accompanied by uddhacca (restlessness) (2 Abhidhamma in Daily Life Chapter 7).
As regards kamavacara sobhana cittas, four of the eight maha-kusala cittas, four of the eight maha-vipakacittas and four of the eight maha-kiriyacittas are accompanied by upekkha.