Conductivity is a measure of a material's ability to carry an electrical current. Conductivity can also be measured for substances such as saline water, or water with significant salt content.
The term saline indicates the presence of concentrations of dissolved inorganic ions, such as salt. The relative magnitude of this concentration determines the salinity of the water.
Brine is water that is heavily saturated with inorganic ions, or salts. By definition, a saline solution becomes brine when its salt concentration hits 45,000 milligrams per liter.
The salt concentration in water determines its conductivity. The greater the salt concentration, the higher the conductivity. Brine, having the largest concentration of salts, consequently has the highest conductivity.