In visual art (drawing, painting, sculpture, etc.), there is a certain style to model the buttocks region in a "butterfly" shape. This method is used, and taught, for example, by the comics and 3D Figure Drawing artist Burne Hogarth.
In the butterfly buttocks style, the two hemispheres of the buttocks are accompanied by two, slightly smaller, bulged masses on the loins that correspond to two areas of fat tissue on the rear of the waist. Unlike the buttocks volumes, these two smaller volumes are not touching but apart, to the sides of the torso, such that there is a depressed area between them on the small of the back, known as the Rhombus of Michaelis.
The butterfly buttocks style are found on both on male and female figures. With adult female figures, the 'loin volumes' are typically a little more pronounced than with male figures. With child figures they are even less, but still there to some degree.
The butterfly buttocks technique can help to get the rear shape of a figure look better and more realistic, but should not be overdone.