standard molality, \(m^{\unicode{x29B5}}\), \(m^{\,\unicode{x26ac}}\)

https://doi.org/10.1351/goldbook.S05918
Chosen value of molality and usually equal to \(1\ \text{mol}\ \text{kg}^{-1}\).
Source:
Green Book, 2nd ed., p. 54 [Terms] [Book]
See also:
PAC, 1994, 66, 533. (Standard quantities in chemical thermodynamics. Fugacities, activities and equilibrium constants for pure and mixed phases (IUPAC Recommendations 1994)) on page 538 [Terms] [Paper]