Egoism refers to excessive interest in one's self; belief that one should be interested in one's self rather than in others.
It is a motive (supposedly underlying all behavior) to increase one's own welfare. The opposite of altruism, which aims to increase another's welfare.
Other /More definition:
Egoism ia defined as a motive (supposedly underlying all behavior) to increase one's own welfare. It is a philosophical doctrine that maintains that people always act out of self-interest.
Egoism is the opposite of Altruism, which aims to increase another's welfare.
Lexicon of Psychology - Terms, Treatments, Biographies,