A vertex is part of a Polygon, and a Polygon is a Primitive in a SOP. A polygon is is formed from a sequence of vertices that are implicitly connected together to form a multi-edge shape in 3D.
Each vertex is an integer index into the Point List, and each Point holds an XYZ position and optional Attributes like Normals and Texture Coordinates.
Each Vertex is a reference to a Point in a Point List. Polygons in a Primitive List are part of the Geometry Detail, which is a part of a SOP.
See also: Geometry Detail, Point, Point List, Point Class, Primitive, Prims Class, Polygon, SOP, SOP Class, SOP to DAT, Script SOP, Point Groups, Primitive Groups, Attributes.