deltahedron

thumb|upright=1.6|The eight convex deltahedra. First row: regular tetrahedron, triangular bipyramid, [[regular octahedron, pentagonal bipyramid. Second row: gyroelongated square bipyramid, regular icosahedron, triaugmented triangular prism, snub disphenoid.]] A deltahedron is a polyhedron whose faces are all equilateral triangles. The deltahedron was named by Martyn Cundy, after the Greek capital letter delta resembling a triangular shape Δ.

Deltahedra can be categorized by the property of convexity. The simplest convex deltahedron is the regular tetrahedron, a pyramid with four equilateral triangles. There are eight convex deltahedra, which can be used in the applications of chemistry as in the polyhedral skeletal electron pair theory and chemical compounds. There are infinitely many concave deltahedra.