What is Thermal wavelength?

Example 10.12 (Argon in a flask)

For argon ($M = 39.95\,\mathrm{g}/\mathrm{mol}$) at $298.15\,\mathrm{K}$, $\Lambda = 16.0\,\mathrm{pm}$, a tenth of an atomic diameter. In $1\,\mathrm{dm}^{3}$, $q^{\mathrm T} = 10^{-3}/(1.600\times10^{-11})^3 = 2.44 \times 10^{29}$ translational states are thermally accessible, far more than the $2.4\times10^{22}$ atoms the flask holds at $1\,\mathrm{bar}$: each state is almost always empty, the condition under which the molecules can be counted as below.