The speed at which wave crests move is called the wave speed or wave velocity.

Here's why:

* Wave crests are the highest points of a wave.

* Wave speed describes how fast a point on the wave, like a crest, travels through the medium.

It's important to note that the wave speed is different from the speed of the particles within the medium. While the wave may travel at a certain speed, the individual particles in the medium only oscillate around their equilibrium positions.