A circumference is a geometric figure consisting of all plane points which are equidistant from a given plane point. This point is called the center. A segment joining any point of a circumference to the center and also its length are called the radius of the circumference.
Around you can see a lot of objects witch geometrical representation is a circumference. A clock dial and a rotated propeller may be drawn as a circumference.
A pair of compasses is an instrument intended for a circumference or an arc construction.