Moral nihilism
Moral nihilism (also known as ethical nihilism) is the meta-ethical view that nothing is intrinsically moral or immoral. For example, a moral nihilist would say that killing someone, for whatever reason, is neither inherently right nor inherently wrong. Moral nihilists consider morality to be constructed, a complex set of rules and recommendations that may give a psychological, social, or economical advantage to its adherents, but is otherwise without universal or even relative truth in any sense.
Moral nihilism is distinct from moral relativism, which does allow for actions to be right or wrong relative to a particular culture or individual, and moral universalism, which holds actions to be right or wrong in the same way for everyone everywhere. Insofar as only true statements can be known, moral nihilism implies moral skepticism.
Forms
According to Sinnott-Armstrong (2006a), the basic thesis of moral nihilism is that "nothing is morally wrong" (§3.4). There are, however, several forms that this thesis can take (see Sinnott-Armstrong, 2006b, pp. 32–37 and Russ Shafer-Landau, 2003, pp. 8–13). There are two important forms of moral nihilism: error theory and expressivism p. 292.