What is described as a 2D representation of geometry in SolidWorks?

In SolidWorks, a 2D representation of geometry is accurately described as a sketch. A sketch is the foundational element used in the 3D modeling process, where designers create 2D shapes using lines, arcs, and other geometrical entities. These entities can then be defined with dimensions and relations, serving as a basis for further features such as extrusions or revolutions that ultimately generate 3D models. The sketching environment allows for precise control and the ability to define shapes needed to build complex designs.

The other options do not represent a 2D geometry specifically. A surface refers to a 3D form that can be created from a 2D sketch but involves additional complexities. A model usually implies a complete 3D representation derived from sketches. An assembly combines multiple parts or models into a single cohesive unit, again moving beyond the concept of a simple 2D representation. Thus, a sketch is the most accurate and direct answer when identifying a 2D geometry in SolidWorks.