These are the mathematical operation which is made out of intersecting coplanar faces. Each face has an ascertainable plane equation, defined as a 3D vector, plus a distance from the origin.
CSG representations
Constructive Solid Geometry (CSG) is the most popular constructive representation. Its primitives are parameterized solids, which may be simple shapes (such as cylinders, cones, and blocks) or more complex features suitable for a particular application domain (such as slots or counter-bored holes).