What type of wave requires a medium to travel through?

Mechanical waves are types of waves that necessitate a medium, such as air, water, or solid materials, to propagate. This is due to the fact that mechanical waves, including sound waves and surface waves on water, transfer energy through the vibrations of particles in the medium itself. As the particles move, they transmit kinetic energy from one particle to the next, allowing the wave to travel.

In contrast, electromagnetic waves, like light and radio waves, do not require a medium for propagation; they can travel through the vacuum of space. Longitudinal and transverse waves refers to the orientation of the motion of particles in relation to the direction of wave travel and can be classified under mechanical waves, but the defining characteristic of requiring a medium pertains specifically to mechanical waves as a whole. Thus, mechanical waves are the correct answer to the question posed.