There are two main types of waves, longitudinal and transverse, depending on the motion of the medium. In transverse waves, the medium moves perpendicular to the direction in which the wave travels. For example, a rope wave is a transverse wave because the rope moves up and down while the wave moves from one end of the rope to the other. Light waves and other electromagnetic waves are also transverse waves. Waves that travel in the same direction that the medium moves are longitudinal waves.
Longitudinal waves require a medium that can be compressed.
You can generate a longitudinal wave in a stretched spring by squeezing and then releasing a few coils at one end of the spring. Waves are usually measured by their amplitude, height, frequency, and wavelength. We can determine the size of a wave by measuring the maximum distance that the wave medium moves from its usual position. For example, as rope waves travel through a rope, the rope forms a wavy line. The highest point on the line is called the wave crest, and the lowest point is the wave trough.