* The ''inner radius'' is the average radius minus the tube radius. It is the shortest possible distance between the origin and points on the torus. The set of points at this minimum distance forms a circle, called the ''inner rim'' or ''inner circle''.
* The ''outer radius'' is the average radius plus the tube radius. It is the maximum distance between the origin and points on the torus. The set of points at this
maixmum distance form a circle, called the ''outer rim'' or ''outer circle''.
* Consider two planes parallel to the plane containing the base circle, with distance from it equal to the tube radius. Both these planes are tangent to the torus, meeting it at circles. These circles are termed the ''top circle'' and ''bottom circle'' (interchangeably). The radius of these circles is equal to the average radius.