Salinity is the saltiness or dissolved salt content of a body of water. Salinity is an important factor in determining many aspects of the chemistryof natural waters and of biological processes within it, and is a thermodynamic state variable that, along with temperature and pressure, governs physical characteristics like the density and heat capacity of the water. The use of electrical conductivity measurements to estimate the ionic content of seawater led to the development of the so-called practical salinity scale 1978 (PSS-78). Salinities measured using PSS-78 do not have units. The 'unit' of PSU (denoting practical salinity unit) is sometimes added to PSS-78 measurements, however this is officially discouraged.