What type of wave is described as moving up and down?

A wave that moves up and down is identified as a transverse wave. In transverse waves, the motion of the medium's particles is perpendicular to the direction of the wave's travel. This can be visualized in phenomena such as waves on a string, where the movement of the string is vertical while the wave travels horizontally.

Transverse waves are characterized by crests (the highest points) and troughs (the lowest points) due to this up-and-down motion. This is different from longitudinal waves, where the particles of the medium move back and forth in the same direction as the wave itself, creating compressions and rarefactions.

Sound waves, although a type of wave, are specifically longitudinal waves, which rely on the vibration of particles in the air (or other mediums) in the direction the sound travels. Electromagnetic waves, like light, can also behave differently and do not require a medium for propagation. However, they propagate in transverse patterns, but in a different context compared to oscillating particles in physical media.

Thus, the key characteristic of the up-and-down movement directly connects to the definition of transverse waves, making it the correct choice in this context.