van der Waals equation

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An equation of state that relates the pressure, volume, and absolute temperature of a gas taking into account the finite size of molecules, and their intermolecular attraction, having the form RT = (P + av⁻²)(v − b), where R is the gas constant, T is the absolute temperature, P is the pressure, v is the volume, and a and b are constants.