pH

Etymology 1
Originally introduced in 1909 by, using the notation pH+ for what he called the “hydrogen ion exponent” (Wasserstoffionenexponent ) of a solution. He may have chosen the symbol p arbitrarily; another suggestion is that it abbreviates. The “H” is the international chemical symbol for the element hydrogen.

Symbol

 * 1)  Measure of the acidity (low pH) or basicity (high pH) of an aqueous solution, equal to the negative logarithm of the concentration of hydronium ions in molars