Noun
600-cell (plural 600-cells)
(geometry) A four-dimensional polytope, analogous to an icosahedron, whose 600 bounding facets are tetrahedra.
In other words: the 30 vertices of the 600-cell which lie at arc distances of 90 degrees on its circumscribed hypersphere from a pair of opposite vertices, are the vertices of an icosidodecahedron. Source: Internet
The wire frame figure of the 600-cell consists of 72 flat regular decagons. Source: Internet