In Russian, юродивый (yurodivy), "holy fool" (our translation), is the name the Orthodox tradition gives to the fool for Christ: the beggar of disordered behavior who lives on the margins and whose apparent foolishness the people take as a sign of holiness. In the book, Rogozhin applies the word to Myshkin on learning that he has never known a woman, and Lebedev repeats it to please him; later, at the party, it comes back in Nastasya's taste for eccentric old men and women.
Where It Appears
Quotes
well, if that is so [...] then you, Prince, turn out to be a complete holy fool, and people like you are loved by God!