Ataraxia (Ἀταραξία) is a Greek term used by Pyrrho and Epicurus for a limpid state, characterized by freedom from worry or any other preoccupation.

For the Epicureans, ataraxia was synonymous with the only true happiness possible for a person. It signifies the detached and balanced state of mind that shows that a person has transcended the material world and is now harvesting all the comforts of philosophy.

From: Sextus Empiricus, Outlines of Pyrrhonism, Translated by R.G. Bury, Harvard University Press, Cambridge, Massachusetts, 1933., p. 19, ISBN 0-674-99301-2