The shape of a KitKat is quite complicated. If you change all the angled faces into horizontal or vertical faces, then a two piece KitKat is an octagon based prism. A four piece KitKat is a 14-gon based prism. Without that approximation it is not even a prism since the cross-section is not exactly uniform at an end and in the middle.
a washer
sphere
convex
Type your answer here... what is the answer
Pentagon
A decagon.
toroid
Any shape is mathematical.
octagon
a cube or cuboid
A six-sided shape is called a hexagon.
A mathematical name would be 213-gon.