Wiktionary
n. A prism with a triangular base.
WordNet
n. a prism whose bases are triangles
Wikipedia
In geometry, a triangular prism is a three-sided prism; it is a polyhedron made of a triangular base, a translated copy, and 3 faces joining corresponding sides. A right triangular prism has rectangular sides, otherwise it is oblique. A uniform triangular prism is a right triangular prism with equilateral bases, and square sides.
Equivalently, it is a polyhedron of which two faces are parallel, while the surface normals of the other three are in the same plane (which is not necessarily parallel to the base planes). These three faces are parallelograms. All cross-sections parallel to the base faces are the same triangle.
Usage examples of "triangular prism".
Far behind and above them, the triangular prism hung huge and blunt and graceless in the center of the pearly ribbon of light, like a long black crystal suspended in milky water.
The Rodewald Building was forty stories of triangular prism with a row of triangular balconies going up each side.
This cut took longer, since it was across the hypotenuse of the triangular prism he was fashioning.
On the edge of the desk facing the lobby was a triangular prism of mahogany and brass inscribed Mr.
The box was a triangular prism a meter long, such as roses are sometimes shipped in.