Definition of pH: 

The term pH comes from Latin. It meas "pondus hydrogenii" hydrogen weight. Another possible meaning is potentia hydrogenii = hydrogen effectivity.
 

The value of  pH is very important regarding  industry, medicine, food sector and agriculture. Although the pH is mostly measured in aqueous solutions it can be also defined in solids (fruits) and in the human body (the value of  pH in the human skin). In order to get appropriate results, it is important to perform the measurement in an object with a proper moisture content. The pH is determined by means of pH indicators or with digital measuring instruments
pH indicators are substances that change color around a particular pH value. With both testing strings and paper indicators less precise results have been discovered. With the digital pH meters you can get a quick and proper results.

pH is defined as minus the decimal logarithm of the hydrogen ion activity in an aqueous solution.^[7] By virtue of its logarithmic nature, pH is a dimensionless quantity.
                                                                 pH = - lga_H+

Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are said to be basic or alkaline.

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