Isothermal Compressibility

The isothermal compressibility Β_T of a material or fluid is the relative (fractional) change in volume per unit increase in pressure at constant temperature, defined by Β_T = -1/V (∂V/∂P)_T and equal to the reciprocal of the isothermal bulk modulus; it quantifies the volumetric susceptibility of a system to pressure changes under isothermal conditions for small perturbations around a given state.