The phrase "gas column" refers to a vertical section of air containing gas. It describes a specific area or space where a gas is present in the air. Full definition
However, limits on the intervening interstellar gas column density from an optical spectrum of HD 61005 in the Na I D lines render this possibility unlikely. (arxiv.org)
M - B applies to our famous gas column when it actually is isothermal — in the no gravity case. (wattsupwiththat.com)
You assert that — under nonphysical (or at least, inconsistent) conditions, that is, zero conductivity — an arbitrarily prepared gas column will relax to one with the DALR. (wattsupwiththat.com)