3-Sphere

A 3-sphere, also called a hypersphere, is a 4-dimensional analogue of an ordinary sphere, the 3-dimensional case of an n-sphere. In 4-dimensional Euclidean space it is the set of points equidistant from a fixed central point, and the region it encloses is called a 4-ball. It is called a 3-sphere because the surface itself is 3-dimensional even though it is curved into a fourth dimension, so moving along it allows motion in three independent directions, making it an example of a 3-manifold.