In SketchUp, section planes cut a model along a plane so that you can peer inside the model – without moving or hiding any geometry. In a 3D model, an active section plane hides everything on one side of the plane.
You can use section planes for all types of applications:
Cut a building horizontally to see the floor plan. In architectural drawing, this two-dimensional top-down cut is called a planimetric view.
Cut a building vertically to see inside the rooms of several floors at once. This type of cut is called a sectional view (not to be confused with SketchUp’s section planes).