The only difference between the Roman Catholic Church and the Holy Orthodox Church for Saint Day May 21 st, is that the Orthodox Church celebrates both Emperor Constantin I ( also known as " equal to the Holy Apostles " ) and his mother Helene on may 21 st, whereas the Catholic Church only celebrates Emperor Constantin I on may 21 st, his mother Helene beeing commemorated or celebrated on a different Saint Day.
" Jour de nom " is more often called in french " fĂȘte de Saint Patron " or simply " fĂȘte " ( Saint Day ), and in Catholic families it is still nowadays celebrated just like a Birthday with presents to the person etc..