Refers to a mindset or attitude of prioritizing one's own interests over others'. Often used in ethical or psychological contexts.
His actions stem from selfishness.
It is important to suppress egoism and serve others.
自己中心 is a more colloquial and direct term for 'self-centeredness', often used in everyday conversation, whereas 利己心 is slightly more literary and abstract.
Compound of 利己 (self-interest) and 心 (heart/mind). The exact historical derivation is uncertain, but the kanji combination directly conveys the meaning of a self-interested mind.