What is Radius ?
Radius is (noun) 1. a line from the centre of a circle to the outside edge We were all asked to measure the radius of the circle. 2. the distance in any direction from a particular central point People within a radius of twenty miles heard the explosion. The school accepts children living within a two-mile radius. 3. the shorter and outer of the two bones in the arm between the elbow and the wrist They found he had fractured his radius. ulna
source: Easier English, Student Dictionary Upper Intermediate Level