Pressure waves refer to a disturbance that travels through a medium, such as air or water, causing changes in pressure along its path. These waves can be created by various means including vibrations, sound, and shockwaves. In medical terms, pressure waves are used to describe the rhythmic expansion and contraction of the chest wall during breathing. This is particularly relevant when discussing conditions such as asthma or chronic obstructive pulmonary disease (COPD).