The term 'round solids' refers to SPHERES, which are three-dimensional objects that have a perfectly round shape. SPHERES are the most symmetrical of all shapes, meaning that they have the same radius from any point on their surface. They are also the only solid shape that has no edges or vertices. SPHERES are found in nature, such as in the form of planets, and are also used in many everyday objects, such as balls and marbles.