The document discusses projections of planes in engineering graphics. It describes two main types of planes: perpendicular and oblique. Perpendicular planes can be perpendicular to both reference planes, perpendicular to one plane and parallel to the other, or perpendicular to one plane and inclined to the other. The document provides examples of projecting rectangles that are parallel to the horizontal plane and perpendicular to the vertical plane, or inclined to the horizontal plane and perpendicular to the vertical plane. It demonstrates how to draw the projections of perpendicular planes in different orientations.