In everyday life, the question is rarely asked, "What is conductivity?"

With the introduction of the SI system of units, "electrical conductivity" became the standard formal term, but in practice the word "conductivity" alone is often used.

Since conductivity is an indicator of how easily current flows through a solution, it depends on the amount of ions and their mobility in that solution.

Conductivity is a measure of how easily electricity can flow. In water, it is the ions that carry the current from one to another. That is, the more Na+ and Cl- there are in the water, the more current is carried, and the higher the conductivity. So if we know the conductivity of a salt water sample, we can calculate how salty the water is. (This is done when converting the salinity to get the value displayed by the Twin conductivity meter).

In summary, the following can be stated: Conductivity is a measure of the ability of a solution to conduct electric current. It is expressed as microsiemens (micro-Siemens per centimeter or µS/cm) or, in higher conductivity levels, as millisiemens. It is also the reciprocal of resistivity. Some industries, such as water treatment, have adopted a measurement known as TDS (Total Dissolved Solids). The TDS value is approximated to conductivity using a multiple factor and is expressed in parts per million (ppm).

An exemplary measurement of conductivity with a pocket tester can be found in the video link below:  Pocket Tester Shop

HORIBA LAQUAtwin Conductivity Meter