Wikipedia
In geometry of 6 dimensions or higher, a triaprism (or triprism) is a polytope resulting from the Cartesian product of three polytopes, each of two dimensions or higher. The Cartesian product of an a-polytope, a b-polytope, and a c-polytope is an (a+b+c)-polytope, where a, b and c are 2-polytopes ( polygon) or higher.
The term triaprism is coined by George Olshevsky, shortened from triple prism, similar to duoprism for the product of two polytopes. John Horton Conway proposed a similar name proprism for product prism, a Cartesian product of two or more polytopes of dimension at least two. The triaprisms are proprisms formed from exactly three polytopes.
The lowest-dimensional triaprisms exist in 6-dimensional space as 6-polytopes being the Cartesian product of three polygons in 2-dimensional Euclidean space.
The smallest is a 3-3-3 triaprism or (triangle-triangle-triangle-triaprism), being the product of three triangles. It has 5-faces (3-3 duoprism prisms), 36 4-faces (9 3-3 duoprisms, 27 3-4 duoprism), 81 cells (27 cubes, 54 triangular prisms), 108 faces (81 squares, 27 triangles), 81 edges, and 27 vertices.