The type of wave where matter moves at right angles to the direction of the wave is called a transverse wave.

Here's why:

* Transverse Waves: In these waves, the particles of the medium oscillate perpendicular (at right angles) to the direction the wave travels. Think of a ripple in a pond – the water molecules move up and down, but the ripple itself travels horizontally.

* Examples: Light waves, electromagnetic waves, and waves on a string are all examples of transverse waves.

Let me know if you'd like to learn more about transverse waves!