What are the different metaethical theories?

Metaethical theories are commonly grouped into five families. Non-cognitivism is the family of views which typically hold that moral statements are expressions of attitudes, as opposed to descriptions of reality. For example, according to emotivism (a non-cognitivist view), when I utter 'Murder is wrong' I am typically doing something akin to saying 'Boo to murder!' That is, I am expressing my feelings. There is no moral knowledge since there are no moral facts to know.The other four families of metaethical theories are cognitivist in nature: they all hold that, typically, moral statements are expressions of beliefs - that is, attempts to describe reality. Error theorists agree with non-cognitivists that there are no moral facts and hence no moral knowledge; however, error theorists argue that when I utter 'Murder is wrong' I am expressing a belief about reality (just like when I say 'That table is brown'), not just expressing an attitude (just like when I say 'Boo to murder!'). For the error theorist, all such moral statements are false, since there are no moral facts. Therefore error theory contrasts with moral realism and subjectivism. Subjectivism is the view that there are moral facts but that these are in some sense subjective or mind-dependent. Moral realism holds that there are objective moral facts. Within moral realism there are naturalist and non-naturalist views: naturalist moral realism holds that the objective moral facts are natural, non-naturalist moral realism that they are non-natural (the clue is in the names!).