What is a holy fool in the Orthodox Church?

St Paul in his epistles describes the gospel as foolishness to those who are perishing. For the Jews, they wanted someone powerful, a messiah to come in and wipe out the Roman horde. And for the Greeks, they wanted something ethereal or otherworldly, something spiritual but not physical. And yet Christ came as foolishness to both. A lowly humble servant, a nobody, a nothingness in terms of the scope of society. And yet we have this continuation of this foolishness that Christ embraced in the holy fools of the Orthodox Church. These are very, very rare saints. In fact, they say that of all of the categories of saints, the holy fools are the most difficult, the hardest path that anyone can embark on.