virial coefficients

Coefficients ( $B , C , ...$ ) in the virial equation of state for a real gas $p V m = R T ( 1 + B V m + C V m 2 + ... )$ where $p$ is the pressure, $V m$ the molar volume, $R$ the gas constant and $T$ the thermodynamic temperature.

Source:

Green Book, 2nd ed., p. 49