Here's a breakdown:

* Wave disturbance: This refers to the change in the medium that the wave carries. For example, in a water wave, it's the change in height of the water surface. In a sound wave, it's the change in air pressure.

* Medium: This is the substance the wave travels through. It could be water, air, a string, or even a vacuum (in the case of light waves).

* Speed: This is the rate at which the disturbance moves through the medium.

It's important to note that the velocity of a wave is not the same as the velocity of the particles in the medium. For example, in a water wave, the water molecules themselves don't travel long distances; they mostly oscillate up and down. The wave's velocity is the speed at which the pattern of those oscillations travels.

The velocity of a wave is often represented by the symbol 'v' and is measured in units of meters per second (m/s) or other units of distance per unit time.