If I am standing on the Earth with my laser and I place two observers on either edge the moon, we may say colloquially that a spot has moved from one observer to the other faster than light can travel, but in actual fact what has really happened is that light has travelled from me to the first observer and then to the second observer at the speed of light, and it is just that my signal to the second observer arrived extremely soon after my signal to the first observer.
Imagine you have a device with two lasers (Laser A and Laser B) that each point down to a white surface. The lasers are one meter from one another, and are calibrated such that Laser B fires exactly 1/(600,000,000)th of a second after Laser A. It might look that the dot is moving faster than light, since light travels at 300,000,000 m/s; however, as we know, nothing went from Point A to Point B.
You can also think about the beacon that a pulsar gives off. We can detect the pulses happening every few seconds-- so what happens when our friend on Alpha Centauri also detects the pulses? The pulsar 'spotlight' is cycling between Alpha Centauri & Earth in a fraction of a second, even though we're 4 lightyears away from eachother.
It's not really FTL, only from a certain point of view. As the author says: "These are all examples of things that can go faster than light, but which are not physical objects. It is not possible to send information faster than light on a shadow or light spot, so FTL communication is not possible in this way. This is not what we mean by faster than light travel, although it shows how difficult it is to define what we really do mean by faster than light travel."
you have a point lightsource in the center of a circle. The radius of the circle is R.
You have a point on a concentric circle with radius R/2. This point is moving on the circumference of this small circle with the speed of light.
If my calculations are right the shadow of the point on the big circle runs with 2*c.