its just a DSM way to catagorise illnesses
1 = main psych diagnosis excluding personality disorders
2 = personality disorders and cognative illness (retardation etc)
3 = somatic illness and disorders
4 = psycho-social problems (think bad home situation, finacial problems, no support networks etc)

and then you have a GAF score that says where youre functioning. they say "normal" is around 75 to 85 as 100 is unattainable.