Answer:
<h2>Longitudinal Waves.</h2>
Explanation:
There are two types of waves: longitudinal and transversal waves.
Longitudinal waves are those where the oscillation and propagation have the same direction, for example, a spring have its oscillation in the same direction of the propagation. This means that both directions are parallel.
On the other hand, transversal waves have these directions differently, like ocean's waves, particles move up and down, while the waves is propagating forward or backwards, this means that both direction are perpendicular.
