1) Christian term 2) True being 
Ousia (ə; οὐσία) is the Ancient Greek noun formed on the feminine present participle of εἶναι (to be); it is analogous to the English participle being, and the modern philosophy adjectival ontic. Ousia is often translated (sometimes incorrectly) to Latin as substantia and essentia, and to English as substance and essence; and (loosely...
a Greek term meaning essence, the essential nature of a thing.