Neurosis is a class of functional mental disorders involving distress but neither delusions nor hallucinations, whereby behavior is not outside socially acceptable norms. It is also known as psychoneurosis or neurotic disorder, and thus those suffering from it are said to be neurotic. Once a common psychiatric diagnosis, the term is no longer part of mainstream psychiatric terminology in the United States, though it continues to be employed in psychoanalytic theory and practice, and in various other theoretical disciplines.