A circle is a set of all points in a plane that are equidistant from a single point; that single point is called the centre of the circle and the distance between any point on circle and the centre is called radius of the circle.

Chord

a chord is an internal segment of a circle that has both of its endpoints on the circumference of the circle.

• the diameter of a circle is the largest chord possible

Secant

a secant of a circle is any line that intersects a circle in two places.

• a secant contains any chord of the circle

Tangent

a tangent to a circle is a line that intersects a circle in exactly one point, called the point of tangency.

• at the point of tangency the tangent line and the radius of the circle are perpendicular