There seems to be a lot of confusion in the definition of ego. So, in this post, I want to give you a clear definition of what ego is, when it is mentioned along with spiritual enlightenment. This definition is consistent with almost all schools of East. First of all, ego is a loose and casual translation of the word ahamkara, which is also referred to dehatma buddhi, or aham vritti. This is little different from what the English word 'ego'  actually means. Ahamkara is just  identifying yourself with everything  that is witnessed by you, including your body, your thoughts, experiences, memories etc. Ahamkara is actually a mental modification which causes the sense of separation. For most of the people in their daily experience, they experientially feel that they are different from the rest of the world. This sense exists both in body and mind. This sense of separation creates an illusory entity which assumes itself to be a doer of actions, thinker of thoughts and the experiencer of experiences. This entity is called ahamkara or ego as it is translated. This assumes itself as the first person and divides the rest of the world into second and third persons. This is what we call as duality. This sense of separation is also what causes craving for fulfillment and fear of destruction.  Once a person is liberated, this sense of independent and separate existence is completely removed. Just as a person experientially felt that he was separate from the world, he now experientially feels and knows that he is no longer separate.  Even after liberation there is a subtle 'I' thought which only serves the liberated man to function in this world. In spite of this subtle 'i' thought, he no longer feels in his experience that he is separate from the reality.