The relationship between pressure and volume in gases is described by Boyle's Law. This principle states that, at constant temperature, the pressure of a gas is inversely proportional to its volume. Thus, when the volume of a gas decreases, its pressure increases, and vice versa, provided that the number of gas molecules remains unchanged. This relationship is fundamental in various applications, including gas laws, respiration, and understanding the behavior of gases in different conditions. The interplay of pressure and volume is essential for predicting how gases will respond to changes in their environment.