what is Ego?

Ego is of two kinds. One is when you are dealing with wordly people and concentrates only on-- I, ME,MY,MINE etc.You create a wall between your self and other people.The second one is when you create a wall between yourself and God.When you say that all the success you have achieved in life is because of your own efforts and not because of His Grace.So long as !I! is there in your mind, Ego is there.

In spirituality, and especially nondual, mystical and eastern meditative traditions, the human being is often conceived as being in the illusion of individual existence, and separateness from other aspects of creation. This "sense of doership" or sense of individual existence is that part which believes it is the human being, and believes it must fight for itself in the world, is ultimately unaware and unconscious of its own true nature. The ego is often associated with mind and the sense of time, which compulsively thinks in order to be assured of its future existence, rather than simply knowing its own self and the present. The spiritual goal of many traditions involves the dissolving of the ego, allowing self-knowledge of ones own true nature to become experienced and enacted in the world. This is variously known as Enlightenment, Nirvana, Presence, and the "Here and Now".

the part of the mind that reacts to reality and has a sense of individuality is ego

Ego would be consider being all about you yourself