Sentence:  The set of all points (x, y) such that (x-1)2&thinsp;+&thinsp;y2 &equals; r2 is a <WSD>circle</WSD> of radius r around the point (1, 0). 
Meaning of the word marked with <WSD> tags:  A two-dimensional geometric figure, a line, consisting of the set of all those points in a plane that are equally distant from a given point (center).