An -D disk (or Disc) of Radius is the collection of points of distance (Closed Disk) or (Open Disk) from a fixed point in Euclidean -space. A disk is the Shadow of a Ball on a Plane Perpendicular to the Ball-Radiant Point line.
The -disk for is called a Ball, and the boundary of the -disk is a -Hypersphere. The standard -disk, denoted (or ), has its center at the Origin and has Radius .
See also Ball, Closed Disk, Disk Covering Problem, Five Disks Problem, Hypersphere, Mergelyan-Wesler Theorem, Open Disk, Polydisk, Sphere, Unit Disk