This is the definition of Room 101 as featured in George Orwell's Nineteen Eighty Four.
It is a torture chamber in the Ministry of Love in which the Party attempts to subject a prisoner to his or her own worst nightmare, fear or phobia.
So I have to ask, why are so many so-called expert guides suffixed/appended with 101? For example, Painting Your House 101.
It seems a strange habit considering the meaning of Room 101, but it seems to have stuck.