|Definition:|| for a system of elementary entities distributed in space, qualifies the length, the area, or the volume of an element of space, all the geometrical dimensions of which are small compared with those of the system under consideration but sufficiently large for the element of space to contain a large number of elementary entities; qualifies also an extensive quantity when summed for all elementary entities within such an element of space
NOTE 1 – The elementary entities can be, for example, elementary particles, molecules, ions, charge carriers, or macroscopic entities such as solid particles or droplets.
NOTE 2 – An extensive quantity (IEV 112-01-06), such as mass, electric charge, or resistance, is additive for disjointed parts of a system. An intensive quantity (IEV 112-01-05), such as mass density, electric charge density, or resistivity, is determinable at any point of a system.
NOTE 3 – The concept can be used to define intensive quantities by the quotient of two quasi-infinitesimal quantities related to the same element of space. Examples are volumic electric charge (IEV 121-11-07) and electric current density (IEV 121-11-11).
NOTE 4 – The term "quasi-infinitesimal" is used to distinguish this concept from that of infinitesimal in the mathematical sense.