In Ancient Greek philosophy, ataraxia —generally translated as "unperturbedness", "imperturbability", "equanimity", or "tranquility"— is a lucid state of robust equanimity characterized by ongoing freedom from distress and worry. In non-philosophical usage, ataraxia was the ideal mental state for soldiers entering battle. Achieving ataraxia is a common goal for Pyrrhonism, Epicureanism, and Stoicism, but the role and value of ataraxia within each philosophy varies in accordance with their philosophical theories. The mental disturbances that prevent one from achieving ataraxia also vary among the philosophies, and each philosophy has a different understanding as to how to achieve ataraxia.