* Transverse Waves: The particles of the medium (in this case, water) move perpendicular to the direction the wave travels. Imagine throwing a pebble into a still pond. The ripples you see are the water molecules moving up and down (perpendicular) as the wave spreads out horizontally.

* Longitudinal Waves: The particles of the medium move parallel to the direction the wave travels. Sound waves are a good example of longitudinal waves.

Important Note: While the wave itself is transverse, individual water molecules don't travel far. They oscillate up and down, but their overall displacement is limited. The energy of the wave is what travels across the surface.