From BiblePortal Wikipedia

Webster's Dictionary [1]

(n.) The conscious and permanent subject of all psychical experiences, whether held to be directly known or the product of reflective thought; - opposed to non-ego.

The Nuttall Encyclopedia [2]

i. e . I and Not-I, or Self and Not-Self), are terms used in philosophy to denote respectively the subjective and the objective in cognition, what is from self and what is from the external to self, what is merely individual and what is universal.