A Prismatoid having planar sides and the same number of vertices in both of its parallel planes. The faces of a prismoid are therefore either Trapezoids or Parallelograms. Ball and Coxeter (1987) use the term to describe an Antiprism.
See also Antiprism, Prism, Prismatoid
References
Ball, W. W. R. and Coxeter, H. S. M. Mathematical Recreations and Essays, 13th ed. New York: Dover, p. 130, 1987.