Coplanar point in affine geometries is any group of points located within the same plane. The property of geometric coplanarity does not just apply to points, but also to objects that have larger dimensions as well like polygons and lines.

Two and one points are always coplanar, as singletons and lines both are on the same plane, though not unique. Three factors will never be non-coplanar, and will define a distinct plane. The rule is that sets with 4 or more point won’t be coplanar.