The law that states that pressure and volume are inversely related in gases is known as Boyle's Law. This fundamental principle of gas laws posits that if the temperature remains constant, an increase in the volume of a gas results in a decrease in its pressure, and vice versa. Mathematically, it can be expressed as P1V1 = P2V2, where P is pressure and V is volume. Boyle's Law plays a vital role in understanding various natural phenomena, including the behavior of lungs during breathing.