What kind of wave is characterized by oscillations that are parallel to the direction of wave travel?

A longitudinal wave is characterized by oscillations that occur in the same direction as the wave travels. In this type of wave, particles of the medium vibrate back and forth along the path of the wave, compressing and rarefying the medium as the wave progresses. This can be observed in sound waves traveling through air, where the air molecules move in the direction of the sound propagation.

In contrast, a transverse wave features particle displacement perpendicular to the wave's direction of travel. Standing waves involve specific patterns of nodes and antinodes and can be found in both transverse and longitudinal waves, while surface waves combine features of both types, such as those seen on water surfaces, where particles move in circular patterns. Thus, the defining nature of longitudinal waves is their parallel oscillation to the direction of wave propagation, distinguishing them clearly from the other types of waves listed.