In descriptive geometry, the section of a solid is the intersection of a plane "Plane (geometry)") with said solid. There are two special types of section; the longitudinal section, when the cutting plane α is parallel "Parallelism (mathematics)") to the main axis of the solid K, and the transverse section when the plane α is perpendicular to the axis of the solid K.

The sections provide information on all the elements that appear hidden in the "Plan (architecture)" plan and main elevations, being very useful in graphic representations of architectural and engineering elements. Forming an almost essential part of the plans of every technical project.