The document discusses different concepts related to clipping in computer graphics including 2D and 3D clipping. It describes how clipping is used to eliminate portions of objects that fall outside the viewing frustum or clip window. Various clipping techniques are covered such as point clipping, line clipping, polygon clipping, and the Cohen-Sutherland algorithm for 2D region clipping. The key purposes of clipping are to avoid drawing objects that are not visible, improve efficiency by culling invisible geometry, and prevent degenerate cases.