Whatever has reality of its own and not merely in potency or in the powers of its causes. That which really is. The fundamental actuality of any being insofar as it is being; it is the being in act. Thus the act of being, or the act of existence by which a substance or an essence is and not only may or can be. It corresponds to the scholastic term esse, namely that something is, and not merely essentia, or what it is.