Self (with a capital 'S') is who I really am: pure spirit, a part of God (along with everyone else), harmless and unharmed, a healed healer healing, who has never been and can never be separated in truth.
(Lower-case 's') self is the perception I am separate, and need to maintain that separation to continue to exist. That is what the ego is. In an attempt to provide a substitute for the real connection craved by the Self with a capital 'S', the ego goes for sex, money, power, prestige, comfort, thrills, and appearance. Other people are threats or opportunities, it believes. The bloated nothingness of this ego is an illusion.