👉 In geometry, an insphere of a polyhedron is a sphere that lies tangent to all its faces. It is often used in the context of 3D space, specifically within a sphere or other solid object. For example, consider a cube with side length \(a\). The cube has six equal squares (faces) as vertices on each face. Each square's center is an insphere because it touches all its faces and forms a circle that includes the centers of those squares.