Osmotic concentration, formerly known as
osmolarity, is the measure of solute
concentration, defined as the number of
osmoles (Osm) of solute per
litre (L) of
solution (osmol/L or Osm/L). The osmolarity of a solution is usually expressed as
Osm/L (pronounced "osmolar"), in the same way that the
molarity of a solution is expressed as "M" (pronounced "molar"). Whereas molarity measures the number of
moles of solute per unit
volume of solution, osmolarity measures the number of
osmoles of solute particles per unit volume of solution.