It is like a freeform NURBS control polygon with some restrictions typically associated with NURBS removed. In the graphic industry it also known as a Subdivision Surface object or SubD for Short. The guys at Pixar originally develeped this technology for modeling organic shapes and you can see it used in all of its animated films.Another way to think about Subdivision surfaces is like a soap bubble where the edges of the control polygon pull on the soap bubble. if you put two edges close together they exert more of a pulling effect and cause the soap bubble to be more curved. You can also increase the curvature of the soap bubble by increasing the weighting on the edge and pulling the soap bubble closer to that edge. If you increase the weighting on the edge all the way to 100% than you create a creased edge that is not smooth.
There are several ways to create SubD objects for use in SolidWorks. Power Surfacing provides several Primitive objects that can be used as starting points, you can use sketches to generate SubDs, or you can import meshobjects directly into the Power Surfacing editor. Also, you can use existing surfaces from the features tree. Finally, the Retopology feature allows you to create high-quality surfaces importing scan data digitized by 3D scanner.