The number of moles of a solute per kilogram of solvent. (Apex)
This the molality (this term is now obsolete).
This concentration is called molality (now an obsolete term).
The number of moles of solute dissolved in 1 L of a solution would be the molarity. As an example, if you had 2 moles of solute in 1 liter the molarity would be 2M.
molarity
Molality is moles of solute per kilogram of solvent. The term is deprecated by NIST, which prefers the less ambiguous "mol/kg".
Concentration
Molality
molarity
(chemistry) the concentration of a substance in solution, expressed as the number moles of solute per kilogram of solventmolality = moles of solute / kg of solvent
Mol is a cocentration unit !
mol/kg