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Octahedron
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<p>In <a href="/facts/Geometry/wTQf5ffQ">geometry</a>, an octahedron (pl.: octahedra or octahedrons) is any <a href="/facts/Polyhedron/UC0p9FTF">polyhedron</a> with eight faces. One special case is the <a href="/facts/Regular_octahedron/G38q92xW">regular octahedron</a>, a <a href="/facts/Platonic_solid/jraREXFD">Platonic solid</a> composed of eight <a href="/facts/Equilateral_triangle/MJomsYDS">equilateral triangles</a>, four of which meet at each vertex. Many types of irregular octahedra also exist, including both <a href="/facts/Convex_set/vdAuJRJl">convex</a> and non-convex shapes. </p>