A circle is a path described by a point in such a way that it is equidistant from a fixed point. The fixed point is called the centre of the circle and the distance from the centre to any point on the circle is called the radius of the circle.

Diameter is a straight line passing through the centre of the circle and joining two points on the circle. 

\(AB =\) Chord, \(PQ =\) Secant line

\(ST =\) Tangent, Shaded part = segment