Class A surfaces is a term used in automotive design to describe a set of freeform surfaces of high efficiency and quality. Although, strictly, it is nothing more than saying the surfaces have curvature and tangency alignment - to ideal aesthetical reflection quality, many people interpret class A surfaces to have G2 (or even G3) curvature continuity to one another (see freeform surface modelling).
Class A surfacing is done using computer-aided industrial design applications. Class A surface modellers are also called "digital sculptors" in the industry. Industrial Designers develop their design styling through the A surface, the physical surface the end user can feel, touch, see etc.
A common method of working is to start with a prototype model and produce smooth mathematical Class A surfaces to describe the products outer body. From this the production of tools and inspection of finished parts can be carried out. Class A surfacing complements the prototype modelling stage by reducing time and increasing control over design iterations.
A class A surface can be defined as any surface that has styling intent.
Class A surfacing / digital sculpting is similar to clay modelling with the added advantage of computing power to change or incorporate design changes in existing/new design.