circular infinity
A circle is two dimensional. The edge of a circle is one dimension. One can travel in one direction along the edge of circle and never reach an end (it appears infinite).
A sphere is three dimensional. The surface of a sphere is two dimensional. One can travel in one direction on the surface of a sphere and never reach an end (it appears infinite).
A hypersphere is four dimensional. The surface of a hypersphere is three dimensional like physical space. One can travel in one direction within a hypersphere's surface and never reach an end (it appears infinite).
Gary