This is a term used to describe those theories of ethical discourse
that contrast ethical sentences
with expressions of beliefs
English translation: these theories say the that primary role of ethical sentences are to express attitudes, effect change, show emotion, and maybe put pressure on people to act. In other words, ethical leverage through expression.
This is not to be confused with emotivism which used the notions of pathos to drive ethical change, the reason that expressivism succeeds emotivism as a description is that the latter term makes no assumptions as to the internal states of the expressors. Ie, notions of truth, and emotion while expressed, are not usually judged as being pivotal or objects of verification in expression within these theories.