The particles of the medium oscillate perpendicular to the direction of wave propagation.

Here's why this is true:

* Transverse waves are waves where the disturbance or oscillation is perpendicular to the direction the wave travels.

* Think of a ripple in water: The water particles move up and down (perpendicular to the surface) as the wave travels horizontally.

Let me know if you'd like more examples or explanations!