"Bounto" is simply the Romaji for 'Bount'
Bounts are living beings who can absorb human souls to become immortal and possess supernatural powers. Their weapons come in the form of 'Dolls', which is their power in a physical manifestation. Like Zanpaktous, they all have unique abilities. However, a Doll can assume both a creature and weapon form. If a Doll is destroyed, the Bount goes with them.