What is Aatma ?

Atma is all-full, beginningless, endless, immeasurable, unchangeable, replete with Sat, Chit, and Anand, decayless, the one essence, the eternal, the undifferentiated, the plenum, the endless, having its face everywhere, the one that can neither be given up nor taken up, the one that can neither be supported nor be made to support, the attributeless, the actionless, the subtle, the changeless, the stainless, the indescribable, the true nature of one’s Atma, above the reach of speech and mind, the one full of Sat, the self-existent, the immaculate, the enlightened, and the incomparable; such is Brahman, one without a second.~ Adhyatma Upanishad