Equanimity is a mind undisturbed by circumstance, not from indifference but from depth. The Bhagavad Gītā calls it yoga; the Buddha made upekkhā one of the divine abidings and factors of awakening; the Stoics sought apatheia; the Jains practise sāmāyika; Christian writers speak of holy indifference.
Equanimity
Evenness of mind in pleasure and pain, gain and loss: a fruit of contemplative practice in every tradition.