The term 'solid square' is a four-letter word that can be used to describe a CUBE. A CUBE is a three-dimensional object with six equal square faces, all of which meet at right angles. It is a regular polyhedron, meaning that all of its faces are the same shape and size. The CUBE is one of the five Platonic solids, which are the only convex polyhedra that have the same number of faces meeting at each vertex.