# Ball (mathematics)

### From Conservapedia

In a metric topology, a **ball** of radius *r* centered at a point *p* is the set of all points at distance at most *r* from *p*. In symbolic notation:

where *d* is the distance function (i.e. metric). Balls are the basic open sets of a metric topology.

If the topology is the Euclidean space, then the boundary (surface) of a ball is a sphere.