Compressibility
In thermodynamics and fluid mechanics, the compressibility (also known as the coefficient of compressibility or, if the temperature is held constant, the isothermal compressibility) is a measure of the instantaneous relative volume change of a fluid or solid as a response to a pressure (or mean stress) change. In its simple form, the compressibility κ {\displaystyle \kappa } (denoted β in some fields) may be expressed as β = − 1 V ∂ V ∂ p {\displaystyle \beta =-{\frac {1}{V}}{\frac {\partial V}{\partial p}}} , where V is volume and p is pressure.