Refers to the self, especially in psychological or philosophical contexts, or one's sense of self-importance.
from Latin
He has a strong ego and rarely listens to others' opinions.
He has a strong ego and won't budge on his opinions.
In psychology, 'ego' refers to the self.
His actions are pure egoism.
Openly showing your selfishness during negotiations is not a good strategy.
You shouldn't decide a child's future path based on the parent's selfish ego.
エゴイスト is the full loanword for 'egoist'; エゴ can be used as its shortened, more casual equivalent when referring to a selfish person.
From Latin 'ego', meaning 'I' or 'self', borrowed into Japanese via Western psychology and philosophy.