Not Otherwise Specified (or NOS) is a subcategory in systems of disease/disorder classification such as ICD-9, ICD-10, DSM-IV, and many others. It is generally used to note the presence of an illness where the symptoms presented were sufficient to make a general diagnosis, but where a specific diagnosis was not made. The DSM-IV, for example, "applies the term not otherwise specified (NOS) to a disorder or disturbance that does not meet the criteria for the specific disorders already discussed". The term was introduced because "it is sometimes impossible for the practitioner completing the diagnostic assessment to categorize all the symptoms that a client is experiencing into one diagnostic category". In the context of mental health diagnoses, four situations have been outlined for which su