Frustum of a pyramid
A frustum of a pyramid (or truncated pyramid) is a pyramid of which the tip has been cut off; hence it has two bases, one at the bottom and a smaller one at the top.
The two bases have the same shape, that is, if the lower base is a quadrilateral, for instance, then the upper base is also a quadrilateral.
However, the sizes of the two base are not the same.
Because the two bases are parallel, the sides of the frustum consists of trapezoids.
The height of the frustum is the shortest distance between the two bases.