'equanimity', also called tatra-majjhattatā, is an ethical quality belonging to the sankhāra-group (s. khandha) and should therefore not be confounded with indifferent feeling (adukkha-m-asukhā vedanā) which sometimes also is called upekkhā (s. vedanā).
upekkhā is one of the 4 sublime abodes (brahma-vihāra), and of the factors of enlightenment (bojjhanga). See Vis.M. IV, 156ff.