Emotivism

The metaethical theory that moral statements express emotions or attitudes rather than stating facts. According to emotivism, saying 'murder is wrong' is equivalent to expressing disapproval, like saying 'murder, boo!'

From Latin 'emotivus' (moving out, stirring) and the suffix '-ism'. Developed by A.J. Ayer and Charles Stevenson in the 1930s-40s as part of logical positivism's attempt to explain the meaning of ethical language.