Disk

An $n$-D disk (or Disc) of Radius $r$ is the collection of points of distance $\leq r$ (Closed Disk) or $<r$ (Open Disk) from a fixed point in Euclidean $n$-space. A disk is the Shadow of a Ball on a Plane Perpendicular to the Ball-Radiant Point line.

The $n$-disk for $n\geq 3$ is called a Ball, and the boundary of the $n$-disk is a $(n-1)$-Hypersphere. The standard $n$-disk, denoted $\Bbb{D}^n$ (or $\Bbb{B}^n$), has its center at the Origin and has Radius $r=1$.

See also Ball, Closed Disk, Disk Covering Problem, Five Disks Problem, Hypersphere, Mergelyan-Wesler Theorem, Open Disk, Polydisk, Sphere, Unit Disk