What is the term for the material through which a wave travels?

The term for the material through which a wave travels is "medium." Waves, whether they are sound waves, water waves, or light waves, require a medium to propagate. For example, sound waves travel through air, water waves move through water, and seismic waves travel through the Earth. The medium can be solid, liquid, or gas, and its properties, such as density and elasticity, significantly affect the speed and behavior of the wave as it moves through it.

Wavefront refers to the line or surface that connects all points of a wave that are in phase, while boundary refers to the interface between two different media, where reflections or refractions may occur. Vibration describes the oscillatory motion of particles in a medium but does not represent the material itself through which the wave travels. Thus, the correct choice highlights the essential concept that waves need a medium to carry their energy from one location to another.