Before finding the word that best describes PK, let's review some important definitions about circles.
Radius: A segment whose endpoints are the center and any point on the circumference of a circle.
Chord: A segment whose endpoints are on the circumference of a circle.
Diameter: A chord that contains the center of the circle.
Secant: A line that intersects a circle in two points.
Tangent: A line in the plane of a circle that intersects the circle in exactly one point — the point of tangency.
Now, consider the given diagram.
We can see that PK is a segment whose endpoints are the center and a point on the circle. Therefore, according to the definitions, we can identify PK as a radius of the circle.
