As shown in the figure on the right, when two secants intersect at a point outside the circle,
there is an interesting relationship between the line segments thus formed.
The blue line in the figure above is called the "secant to the circle c".
As you move one of the points P,Q, the secant will change accordingly. If the two points coincide at the same point, the secant becomes a tangent, since it now touches the circle at just one point.
The line segment inside the circle between P and Q is called a chord.
As shown in the figure on the right, when two secants intersect at a point outside the circle,
there is an interesting relationship between the line segments thus formed.
See Intersecting Secants Theorem for a detailed explanation.