Ousia (/ˈuːziə, ˈuːsiə, ˈuːʒə, ˈuːʃə/; Ancient Greek: οὐσία) is a philosophical and theological term, originally used in ancient Greek philosophy, then later in Christian theology. It was used by various ancient Greek philosophers, like Plato and Aristotle, as a primary designation for philosophical concepts of essence or substance. In contemporary philosophy, it is analogous to English concepts of being and ontic. In Christian theology, the concept of θεία ουσία (divine essence) is one of the most important doctrinal concepts, central to the development of trinitarian doctrine.