.... the term "galleon" has taken multiple meanings and is not a precise class of sailing ship.
        Nonetheless, it is arguable to define a galleon has having a "flushed deck without castles."

        The ships officially referred to as galleons by some British museums certainly have both fore and after castles, although
        somewhat reduced in height compared to carracks. Indeed, castles remained as part of the architecture for a couple of 
        centuries - up to the time of the clipper ships.

        It seems that the other main difference is that the forecastle of a carrack protruded beyond the bow as an overhang, while that of the
        galleon was set further aft, allowing room for a long, triangular beak at the stem.

        For a color picture that demonstrates this point, you might want to visit the site at:
        http://www.thabebanss.qld.edu.au/studentprojects/sailage/sailgallery.htm