The Collaborative International Dictionary of English v.0.48:

molality \molality\ n. (Chem.)
   A measure of concentaration of substances in mixtures, 1
   molal being the concentration of a solution containing 1 mole
   of solute per 1000 grams of solvent. Compare molar.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

molality
    n 1: concentration measured by the number of moles of solute per
         kilogram of solvent [syn: molality, molal
         concentration]