Near to me the defination of ego is "i".
When you start thinking about yourself and think that i am the most smartest person on the earth and all other peoples are wrong only i am right, then you are on the peek of ego.
Is ego good or bad.?
Ego is good thing when it increase positive things in you and makes you a good person but ego is bad when it makes you a negative person and creates negative things in you. To much ego destroyed yourself.
Does It Affect on our life.?
Ego have the power to detroy everything. Every rlationship works or breaks due to EGO. Ego has the ability to breaks our relations. if we possess too much egotism, we end up ruining every relationship. So always give importance to your relations not your ego, because true relations are God gifted once they leave us our life is empty.
On the other side if someone give you more importance then his or her ego its does not mean he has no ego it means near to him or her relations are more important then ego. If you have such kind of person in your life respect him or her.