‘Altruistic’ designates any action which is deemed morally good, but which carries or implies no obligation to act.
This is distinct from other moral actions which are designated 'right' or 'wrong'. An action with the former designation carries a positive obligation to action; an action with the latter designation carries a negative oblication. Altruistic actions are generally considered to have no obligatory element at all; they are above and beyond ordinary moral expectations. They are also known as supererogatory actions.