Slicing a 3D space figure with a plane creates a cross section. The cross section is the part of the plane that overlaps with the 3D figure.
Cutting different geometric figures with a plane or cutting the same geometric figures from different angles or positions may create cross sections of different shapes. The following are some examples.
The cross section formed when a plane intersects a sphere through the sphere's center is a circle often referred to as a great circle of the sphere.
The cross section formed by the intersection of a plane that is parallel to the base of a regular triangular prism is an equilateral triangle.
When a plane intersects a cone at different angles or positions, one of four cross-sectional shapes is formed.