Noun
bipyramid (plural bipyramids)
A dipyramid.
A concave bipyramid has a concave interior polygon. : The face-transitive regular bipyramids are the dual polyhedra of the uniform prisms and will generally have isosceles triangle faces. Source: Internet
An extra axial straw is added which doesn't exist in the simple polyhedron An n-gonal bipyramid or dipyramid is a polyhedron formed by joining an n-gonal pyramid and its mirror image base-to-base. Source: Internet
A regular icosahedron is a gyroelongated pentagonal bipyramid and a biaugmented pentagonal antiprism in any of six orientations. Source: Internet
In this nomenclature, an octahedron would be a square bipyramid, a cuboctahedron would be a triangular gyrobicupola, and an icosidodecahedron would be a pentagonal gyrobirotunda. Source: Internet
The second type is a rhombic bipyramid. Source: Internet