What is a 3D circle called

A 3D circle is called a sphere, which is the three-dimensional equivalent of a circle extended into space. While a circle is a flat, two-dimensional shape where all points are equidistant from a center point on a plane, a sphere is a perfectly round three-dimensional object where all points on its surface are equidistant from a center point in space. The sphere represents the set of all points at a fixed distance (the radius) from its center in three-dimensional space.

The terminology distinction is important: "circle" specifically refers to the 2D shape, while "sphere" refers to the 3D object. In everyday language, people sometimes loosely call spherical objects "circles" (saying "draw a circle" when they mean a sphere in a 3D modeling program), but mathematically and technically, these are distinct entities with different properties and formulas. Circles have circumference (2πr) and area (πr²), while spheres have surface area (4πr²) and volume (4/3πr³). Examples of spheres include basketballs, planets, marbles, and bubbles—objects with depth and volume. When working in mathematics, physics, computer graphics, or engineering, using precise terminology prevents confusion: specify "circle" for 2D contexts and "sphere" for 3D objects. This clarity becomes especially important in technical fields where the difference between two- and three-dimensional calculations dramatically affects results and where ambiguous terminology could lead to significant errors.