The "Pressure-Volume Relationship" describes how the pressure of a gas changes with its volume, often illustrated by Boyle's Law. This law states that, at a constant temperature, the pressure of a gas is inversely proportional to its volume. This means that if the volume decreases, the pressure increases, and vice versa. This relationship is crucial in various fields, including physics and engineering. It helps explain how gases behave in different conditions, such as in pneumatics or when using syringes. Understanding this concept is essential for applications like designing engines and predicting how gases will react under pressure changes.