A wave in which the medium vibrates perpendicular to the direction of motion is called a transverse wave.

Here's a breakdown:

* Transverse wave: The particles of the medium move up and down (or side to side), while the wave itself travels horizontally. Think of a ripple on the surface of water or a wave on a rope.

* Longitudinal wave: The particles of the medium vibrate parallel to the direction of motion. Think of a sound wave, where the air molecules compress and expand in the same direction the wave travels.