Different Geometry Types and Formats in CAD

Constructive solid geometry (CSG) is a modeling technique used in CAD systems to create a complex geometry by combining parametric features and Boolean operations. CSG presents a solid or surface that appears visually complex, but is actually little more than cleverly combined or decombined objects (primitives, extrusion, revolution, sweep, filet, chamfer, shaft, ...).

Boundary Representation is a method for representing shapes using the limits. it is often abbreviated as B-Rep or BREP in CAD modeling. A solid is represented as a collection of connected surface elements, the boundary between solid and non-solid. Boundary representation models are composed of two parts: topology (faces, edges and vertices) and geometry (surfaces, curves and points). An edge is a bounded piece of a curve and a vertex lies at a point. A face is a bounded portion of a surface. These geometry is commonly called "precise geometry".
Manifold solids have the property that, at every point on the boundary, a small enough sphere around the point is divided into two pieces, one inside and one outside the object. Non-manifold models break this rule.

Tessellation is a triangular approximation to represent precise geometry in a light representation. SAG parameter is set to control the approximation by defining the maximum distance between the triangle and the surface.