Final answer:
The principle that describes how gaseous volume is inversely proportional to pressure is known as Boyle's Law.
Step-by-step explanation:
The principle stating that gaseous volume inversely relates to pressure defines Boyle's Law. Boyle's Law indicates that at a constant temperature, the volume of a fixed amount of a gas is inversely proportional to its pressure. This is a foundational concept in chemistry and physics explaining how gases behave under different pressures when the temperature is held constant.