Simplify the following text for a Grade 4 native English-speaking person.
Original: The English word of Greek origin `` callipygian '' indicates someone who has beautiful buttocks . However , the qualities that make buttocks beautiful or well-formed are not fixed , as sexual aesthetics of the buttocks vary considerably from culture to culture , from one period of fashion to another and even from person to person .
Simplified: Buttocks can also be called a `` butt '' .