Concentration count per volume Amount of substance or a count/number of items per unit volume. Concentration impliles the amount of one substance/item within another substance. Chemistry QUDT http://qudt.org/vocab/quantity#AmountOfSubstancePerUnitVolume Distinct from inverse volume in that there is something specific being counted within each unit volume. Inverse volume implies a truly dimensionless numerator. ODM2 Units Type Controlled Vocabulary ODM2 Working Group A vocabulary for describing the type of the Unit or the more general quantity that the Unit represents.