The ego is your consciousness of your own identity, or the
conscious mind. Basically, your ego is related to your confidence
level; if you have a big ego, your confidence is high, and visa
versa. Additionally, having an ego can mean having an inflated
feeling of pride or self-worth.
It can mean someone who's ego is inflated, i.e. they are
overconfident or arrogant, they think very highly of
deflated ego, the opposite, means someone who is underconfident,
has low self-esteem, self-doubts a lot.