NURBS
NURBS stands for Non-Uniform Rational B-Spline. NURBS objects are objects created by object generators. They themselves have no inherent geometry; rather, they use other objects to create (or generate) a new object. NURBS can make a pipe out of a circle, a vase out of a squiggle, a vine from a line and a profile, and a head from a cube.

SPLINES
The primary building tools of most NURBS objects are splines. Splines contain points (or vertices) that still have no geometry of their own. These points define the shape (linear, curvy) of the lines between the points. Further, the lines that connect these points together also have no inherent geometry; the manual describes them as 'infinitely thin." The idea is that splines will never render. They are simply a collection of points connected by lines that exist within three-dimensional space. The lines that connect these varying points in space create a shape through a process referred to as interpolation. Although splines themselves have no geometry, they can be used to create a wide variety of geometry.

PRIMITIVES
Primitives are objects that C4D creates via mathematical formulas that create a shape based on determined values. Because of this dynamic mathematical nature, most primitives in C4D are said to be parametric, meaning the parameters of these primitive objects can be easily changed. What this means is that although C4D actually uses polygons to display the objects in the Editor, primitives don't actually have any polygons of their own until rendered. The benefit of this is similar to NURBS objects: by altering the parameters, you can quickly get new shapes without having to alter the object at the polygonal level. The drawback is that you can only alter the shape according to C4D's parameter variables.

FILLETS
Fillets are rounded sections or corners of shapes. Almost all of the primitives allow you to activate the Fillets option to make primitive forms less blocky and hard-edged. This is where some of the power of primitives really begins to emerge. To create the rounded edges you would need to manually shift an awful lot of polygons to create this rounded shape. However, with parametric primitives, you simply double-click on the blue Primitive icon and activate the Fillet button within the dialog box and then edit the values set in the input fields to change the depth of the rounded edge