Full Idea
The Greatest Happiness Principle holds that actions are right in proportion as they tend to promote happiness, wrong as they tend to produce the reverse of happiness. By happiness is intended pleasure, and the absence of pain.
Gist of Idea
Actions are right if they promote pleasure, wrong if they promote pain
Source
John Stuart Mill (Utilitarianism [1861], Ch.2)
Book Reference
Mill,John Stuart: 'Utilitarianism (including On Liberty etc)', ed/tr. Warnock,Mary [Fontana 1962], p.257