In geometry, the midsphere or intersphere of a polyhedron is a sphere which is tangent to every edge of the polyhedron. That is to say, it touches any given edge at exactly one point. Not every polyhedron has a midsphere. It is so-called because it is between the inscribed sphere (touches every face) and the circumscribed sphere (touches every vertex). The radius of this sphere is called the midradius. Important classes of polyhedra which have interspheres include: