There is no IQ number associated with the term idiot in
psychological diagnoses. We simply don't refer to people in that
manner. However, they did in the past, people were labelled an
idiot at the 20 range. However, those were different times, and the
term idiot didn't really carry the stigma and insult that it does
today. Today we refer to those among that range as profoundly
mentally retarded. Even though these terms exist in the DSM IV TR,
they are not particularly useful and will likely change with the
DSM V.