What is definition of compressional?

waves:

Compressional waves, also known as longitudinal waves, are types of mechanical waves that occur when particles in a medium vibrate back and forth in the same direction that the wave is moving. These waves occur in all types of media – solid, liquid, and gas – and are characterized by areas of compression and rarefaction, where the medium's density increases and decreases, respectively.

The speed at which compressional waves travel through a medium is dependent on the density of the medium and the elasticity of its particles. This means that these waves travel faster in denser materials and slower in less dense materials.

Examples of compressional waves include sound waves, seismic waves, and pressure waves in fluids. They are utilized in a variety of applications, including communication, medical imaging, and exploration of the Earth's subsurface.