Back-face culling is a method in computer graphics programming which determines whether a polygon of a graphical object is visible. If not visible, the polygon is "culled" from rendering process, which increases efficiency by reducing the number of polygons that the hardware has to draw.
The vertices of front-facing polygons wind in a clockwise fashion, so polygons that face away from the camera are in a counter-clockwise order relative to the current view. When back-faces are culled, these polygons are not drawn.
Note: The process is similar to clipping, which determines if polygons are in the camera's field of view at all, and if not, are not rendered.