The different forms of egoism

 Egoism can be a descriptive or a normative position. 

Psychological egoism, the most famous descriptive position, claims that each person has but one ultimate aim: her own welfare.

 Normative forms of egoism make claims about what one ought to do, rather than describe what one does do. 

Ethical egoism claims I morally ought to perform some action if and only if, and because, performing that action maximizes my self-interest. 

Rational egoism claims that I ought to perform some action if and only if, and because, performing that action maximizes my self-interest. (Here the “ought” is not restricted to the moral “ought”.)