What type of wave requires a medium to travel through?

A mechanical wave is a type of wave that requires a material medium to travel through.

Mechanical waves transfer energy by causing particles in a substance to oscillate around equilibrium positions. The medium can be a solid, liquid, or gas, but it must have properties such as elasticity and inertia. Sound waves, water waves, and seismic waves are familiar examples.

Mechanical waves can be transverse, longitudinal, or surface waves. In a transverse wave, particles move perpendicular to the direction of propagation; in a longitudinal wave, they move parallel to it, producing compressions and rarefactions. Sound in air is primarily longitudinal, while waves on a stretched string are transverse.

The key contrast is with electromagnetic waves, such as light and radio waves, which can propagate through a vacuum. A mechanical wave may travel across a large distance, but the material itself generally moves only locally as energy passes through it. “Matter wave” is a quantum concept associated with particles, not the standard answer to this classification question.