Unit sometimes used in the description of the total ozone in a column of air overhead. It is given as the thickness (in units of 10E-3 cm or 10E-5 m) of that layer which would be formed by the total ozone in a column reduced to the pressure of 760 Torr and temperature of 0°C.
Source:
PAC, 1990, 62, 2167. 'Glossary of atmospheric chemistry terms (Recommendations 1990)' on page 2185 (https://doi.org/10.1351/pac199062112167)