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

https://doi.org/10.1351/goldbook.S05918

Chosen value of molality and usually equal to 1 mol kg-1.

Source:
Green Book, 2^nd ed., p. 54 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf)

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 (https://doi.org/10.1351/pac199466030533)