The term pH stands for "potential of hydrogen." It is a measure of the concentration of hydrogen ions (H⁺) in a substance, which determines its acidity or basicity

. More specifically, in modern chemistry, the "p" in pH represents the negative logarithm (base 10) of the hydrogen ion concentration, so pH = -log[H⁺]

. The pH scale ranges from 0 to 14:

• A pH of 7 is neutral (pure water).
• Values less than 7 indicate acidity (more hydrogen ions).
• Values greater than 7 indicate alkalinity or basicity (fewer hydrogen ions)

The concept was introduced by Danish biochemist Søren Peder Lauritz Sørensen in 1909 to quantify acidity in solutions

. In summary, pH measures how acidic or basic a solution is by expressing the concentration of hydrogen ions, with the name reflecting "potential of hydrogen" or the logarithmic measure of hydrogen ion activity.