The type of wave where particles in a medium move perpendicular to the direction the wave travels is called a transverse wave.

Here's a breakdown:

* Transverse wave: Imagine shaking a rope up and down. The wave travels along the rope, but the rope itself moves up and down, perpendicular to the direction of the wave's travel.

* Longitudinal wave: In a longitudinal wave, the particles of the medium move parallel to the direction of wave travel. A good example is sound waves, where the air molecules compress and expand in the same direction that the sound travels.

Let me know if you'd like more detail on either type of wave!