Circle

A circle is the locus of a point which moves in a plane in such a way that its distance from a fixed point remains constant.

SECANT:

A line, which intersects a circle in two distinct points, is called a secant.

TANGENT:

A line meeting a circle only in one point is called a tangent to the circle at that point.

The point at which the tangent line meets the circle is called the point of contact.

LENGTH OF TANGENT:

The length of the line segment of the tangent between a given point and the given point of contact with the circle is called the length of the tangent from the point to the circle.