Tatramajjhattatā

Tatramajjhattatā is a Buddhist term that is translated as "equanimity", "neutrality of mind", etc. In the Theravada tradition, it is defined as a mental attitude of balance, detachment, and impartiality.
Tatramajjhattatā is identified as:

One of the twenty-five beautiful mental factors within the Theravada Abhidharma teachings
A synonym of upekkha

Explanations

Theravada

Bhikkhu Bodhi explains:
The Visuddhimagga states about equanimity:
Nina van Gorkom explains: